1. September 11, 2001 - Thanks to the power of the web and live broadcasts on television, the conspiracy theories surrounding the events of 9/11 - when terrorists attacked the World Trade Centre in New York and the Pentagon in Washington - have surpassed those of Roswell and JFK in traction. Despite repeated claims by al-Qaeda that it planned, organised and orchestrated the attacks, several official and unofficial investigations into the collapse of the Twin Towers which concluded that structural failure was responsible and footage of the events themselves, the conspiracy theories continue to grow in strength.

At the milder end of the spectrum are the theorists who believe that the US government had prior warning of the attacks but did not do enough to stop them. Others believe that the Bush administration deliberately turned a blind eye to those warnings because it wanted a pretext to launch wars in the Middle East to usher in another century of American hegemony. A large group of people - collectively called the 9/11 Truth Movement - cite evidence that an airliner did not hit the Pentagon and that the World Trade Centre could not have been brought down by airliner impacts and burning aviation fuel alone. This final group points to video evidence which they claim shows puffs of smoke - so-called demoliton squibs - emerging from the Twin Towers at levels far below the aircraft impact zones and prior to the collapses. They also believe that, on the day itself, the US air force was deliberately stood down or sent on exercises to prevent intervention that could have saved the lives of nearly 3,000 people.

Many witnesses - including firemen, policemen and people who were inside the towers at the time - claim to have heard explosions below the aircraft impacts (including in basement levels) and before both the collapses and the attacks themselves. As with the assassination of JFK, the official inquiry into the events - the 9/11 Commission Report - is widely derided by the conspiracy community and held up as further evidence that 9/11 was an "inside job". Scientific journals have consistently rejected these hypotheses.

Picture: AP

2. The assassination of John F Kennedy - The 35th President of the United States was shot on Friday, November 22, 1963, in Dallas, Texas at 12.30pm . He was fatally wounded by gunshots while riding with his wife - Jacqueline Bouvier Kennedy - in a motorcade. The ten-month investigation of the Warren Commission of 1963 to 1964, the United States House Select Committee on Assassinations (HSCA) of 1976 to 1979, and other government investigations concluded that the President had been assassinated by Lee Harvey Oswald - who was himself shot dead by Jack Ruby while in police custody.

But doubts about the official explanation and the conclusion that Oswald was the lone gunman firing from the Texas Book Depository overlooking Dealey Plaza where Kennedy was hit surfaced soon after the commission report. Footage of the motorcade taken by Abraham Zapruder on 8mm film supported the growing belief that at least four shots were fired - not the three that the Warren Commission claimed. The moments of impact recorded on the film also suggested that at least one of the shots came from a completely different direction to those supposedly fired by Oswald - evidence backed up by testimony of several eye witnesses. Many believed that several shots were fired by gunmen hiding behind a picket fence on a grassy knoll overlooking the plaza.

The assassination is still the subject of widespread speculation and has spawned numerous conspiracy theories, though none of these has been proven. In 1979, the House Select Committee on Assassinations (HSCA) found both the original FBI investigation and the Warren Commission Report to be seriously flawed. The HSCA also concluded that there were at least four shots fired and that it was probable that a conspiracy existed. However, later studies, including one by the National Academy of Sciences, have called into question the accuracy of the evidence used by the HSCA to support its finding of four shots.

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3. A flying saucer crashed at Roswell in 1947 - The event that kick-started more than a half century of conspiracy theories surrounding unidentified flying objects (UFOs). Something did crash at Roswell, New Mexico, sometime before July 7, 1947 and - at first - the US authorities stated explicitly that this was a flying saucer or disk - as shown by the splash story on that day's Roswell Daily Record, pictured. Numerous witnesses reported seeing metallic debris scattered over a wide area and at least one reported seeing a blazing craft crossing the sky shortly before it crashed. In recent years, witnesses have added significant new details, including claims of a large military operation dedicated to recovering alien craft and aliens themselves, at as many as 11 crash sites, and alleged witness intimidation. In 1989, former mortician Glenn Dennis claimed that he was involved in alien autopsies which were carried out at the Roswell air force base.

The conspiracy theory has been fanned by the US military repeatedly changing its story. Within hours of the army telling reporters that it had recovered a crashed saucer, senior officers insisted that the only thing that had fallen from the sky had been a weather balloon. A report by the Office of the Secretary of the Air Force released in 1995, concluded that the reported recovered material in 1947 was likely debris from a secret government program called Project Mogul, which involved high altitude balloons meant to detect sound waves generated by Soviet atom bomb tests and ballistic missiles. A second report, released in 1997, concluded that reports of alien bodies were likely a combination of innocently transformed memories of military accidents involving injured or killed personnel, and the recovery of anthropomorphic dummies in military programs like Project High Dive conducted in the 1950s.

Since the late 1990s the debate about Roswell has polarised with several former pro-UFO researchers concluding that the craft was, indeed, part of a US military project and that it was, most likely, some sort of weather balloon. But further evidence has emerged - notably a signed affidavit by Walter Haut, the Roswell Army Air Field public affairs officer who had drafted the initial press release on July 8, 1947. Haut says in the affidavit -signed in 2002 - that he saw alien corpses and a craft and that he had been involved in a military cover up. Haut died in 2005.

4. Nasa faked the moon landings - People who think that the Apollo moon landings were not all that they seemed at the time believe that Nasa faked some or all of the landings. Some of the theories surrounding this subject are that the Apollo astronauts did not land on the Moon; Nasa and possibly others intentionally deceived the public into believing the landings did occur by manufacturing, destroying, or tampering with evidence, including photos, telemetry tapes, transmissions, and rock samples; and that Nasa and possibly others continue to actively participate in the conspiracy to this day. Those who think that Nasa faked some or all of the landings base their theories on photographs from the lunar surface which they claim show camera crosshairs partially behind rocks, a flag planted by Buzz Aldrin moving in a strange way, the lack of stars over the lunar landscape and shadows falling in different direction. Many commentators have published detailed rebuttals to the hoax claims, and these theories have been generally discounted but belief in them - particularly on the web - persists.

Picture: AP

5. The Illuminati and the New World Order - A conspiracy in which powerful and secretive groups (the Illuminati, the Bilderberg Group and other shadowy cabals) are plotting to rule mankind with a single world government. Many historical events are said to have been engineered by these groups with one goal - the New World Order (NWO). The groups use political finance, social engineering, mind control, and fear-based propaganda to achieve their aims. Signs of the NWO are said to be the pyramid on the reverse of the Great Seal of the United States, inset, strange and disturbing murals at Denver International Airport, pictured, and pentagrams in city plans. International organisations such as the World Bank, the IMF, the European Union, the United Nations, and Nato are listed as founding organisations of the New World Order.

6. The Jesus conspiracy - The theory that launched a blockbusting novel (The Da Vinci Code), a film of the same name and a plagiarism battle in the courts (with the authors of the Holy Blood and holy grail). Those who believe in this - and they seem to number in their millions - think that Jesus married Mary Magdalene, had one or more children, and that those children or their descendants emigrated to southern France. Once there, they intermarried with the noble families that would eventually become the Merovingian dynasty, whose special claim to the throne of France is championed today by a secret society called the Priory of Sion.

7. Diana, Princess of Wales, was murdered - Why won't this one go away? Despite an official inquiry that found no evidence of a plot by MI6 or any other entity to murder the princess and Dodi Fayed in 1997, fevered speculation continues. The theory is that rogue elements in the British secret service decided that Diana's relationship with Fayed was a threat to the monarchy and, therefore, to the British state. A plot was hatched in which a white Fiat Uno carrying agents was sent to blind and disorientate driver Henri Paul as he sped through the Paris underpass pursued by photographers. Later, Paul's blood was switched with a sample of somebody who had drunk a lot of alcohol. The trouble with the theory? Not a shred of evidence exists to support it.

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8. Elvis Presley faked his own death - What can we say? A persistent belief is that "the King" did not die in 1977. Many fans persist in claiming he is still alive, that he went into hiding for various reasons. This claim is allegedly backed up by thousands of so-called sightings. The main reason given in support of the belief that Presley faked his death is that, on his grave, his middle name Aron is spelt as Aaron. But "Aaron" is actually the genuine middle name for Presley. Apparently, either Presley or his parents tried to change the name to "Aron" to make it more similar to Presley's stillborn twin, Jesse Garon Presley. Two tabloid newspapers ran articles covering the continuing "life" of Presley after his death, in great detail, including a broken leg from a motorcycle accident, all the way up to his purported "real death" in the mid 1990s.

9. Operation Northwoods - A genuine conspiracy involving a plan by the Joint Chiefs of Staff to launch a fake Cuban terror campaign on American soil to persuade the US public to support an invasion against Castro. The plan involved bombings and the simultaneous hijacking and blowing up of American airliners. The operation was quashed by President Kennedy leading many to speculate that it was linked to his assassination a year later. The plan has also been linked by theorists who believe that the September 11, 2001 attacks were a so-called "inside job" because of the use of airliners

10. MK-ULTRA - The code name for a covert mind-control and chemical interrogation research programme, run by the Office of Scientific Intelligence. The programme began in the early 1950s, continuing at least through the late 1960s, using US citizens as test subjects. Project MK-ULTRA was brought first to wide public attention in 1975 by Congress and by the Rockefeller Commission. Investigative efforts were hampered by the fact that CIA Director Richard Helms ordered all MK-ULTRA files destroyed in 1973. Although the CIA insisted that MK-ULTRA-type experiments were abandoned, CIA veteran Victor Marchetti has stated in various interviews that the agency routinely conducts disinformation campaigns and that CIA mind control research continued. In a 1977 interview, Marchetti specifically called the CIA claim that MK-ULTRA was abandoned a "cover story". Conspiracy theorists believe that MK-ULTRA was behind many so-called black-ops: Lawrence Teeter, the attorney for Sirhan Sirhan, the man convicted of the assassination of Robert Kennedy, pictured, believed Sirhan was operating under MK-ULTRA mind control techniques. Furthermore, Jonestown, the location in Guyana where members of the Jim Jones cult and Peoples Temple committed mass suicide, was thought to be a test site for MK-ULTRA medical experiments.

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11. North American Union - The North American Union (NAU) is a theoretical regional union of Canada, Mexico and the United States similar in structure to the European Union, sometimes including a common currency called the amero. Theorists who believe that the three countries are planning for this believe that it is part of a global conspiracy to set up something called the New World Order (NWO). Officials from all three nations have repeatedly denied that there are plans to create a NAU although the idea has been proposed in academic circles, either as a union or as a North American community as proposed by the Independent Task Force on North America. The amero received support in 1999 from Canadian economist Herbert Grubel, a senior fellow of the Fraser Institute think-tank, in a book entitled The Case for the Amero. Robert Pastor, vice-chairman of the Independent Task Force on North America, supported Grubel's conclusions in his 2001 book Toward a North American Community, stating that: "In the long term, the amero is in the best interests of all three countries".

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12. Shakespeare was somebody else - Who really was the English language's greatest writer? Among the numerous alternative candidates that have been proposed Francis Bacon, Christopher Marlowe, William Stanley (6th Earl of Derby) and Edward de Vere (17th Earl of Oxford), are the most popular. Theorists believe there is a lack of evidence proving that the actor and businessman sometimes known as Shaksper of Stratford was responsible for the body of works that bear his name. Very little biographical information exists about Shakespeare.

13. The disappearance of Shergar - On February 8, 1983, a group of men wearing balaclavas and armed with guns turned up at the Ballymany Stud Farm in Co Kildare, Ireland and took a hostage – Jim Fitzgerald, the stud's head groom. "We've come for Shergar," they said. "We want £2m for him." Shergar was arguably the greatest racehorse to have ever lived. But 25 years after he was kidnapped from Ballymany the mystery of exactly what happened to him after he was snatched that night still lingers. The theories are numerous with the IRA, Colonel Gadaffi and the Mafia featuring among the most lurid. One story suggests that the IRA kidnapped the horse for Gadaffi in return for weapons. Another suggests that the New Orleans mafia took him.

Picture: GETTY IMAGES

14. Paul is dead - “Paul is dead” is an urban legend alleging that Paul McCartney died in a car crash 1966 and was replaced by a look-alike and sound-alike. "Evidence" for McCartney’s death consists of “clues” found among the Beatles’ many recordings. Hundreds have been cited at various times by various people. They include statements allegedly heard when a song is played backwards, symbolism found in obscure lyrics, and ambiguous imagery on album covers. A few of them are well known, such as the fact that McCartney is the only barefooted Beatle and is out of step with the others on the cover of Abbey Road, pictured.

Picture: Redferns

15. The July 7, 2005 Tube bombings - One of the supposed mysteries surrounding the 7/7 attacks is this image, used by several news outlets, of the bombers entering Luton station on their way to London at around 7.20am on July 7. Theorists claim this image is fake because the man in the white hat - believed to be Mohammed Sidique Khan - has been electronically placed on the picture after it was taken. They claim that it shows his arm behind a railing while the rest of his body is in front and that the bar behind his head goes across and in front of his face. Theorists postulate, among other things, that the bombs which went off on the Tube trains were actually under the floors of the vehicles and not in the alleged plotters' back packs.

Picture: PA