The TV4 programme Kalla Fakta, which commissioned the survey, will on Sunday address the subject of the Truth Movement, an international group which espouses the conspiracy theory that the terror network al-Qaida was not behind the September 11th attacks.

The movement, also known as the “September 11th research community” argues that it was in fact the US government that staged the attacks, which claimed the lives of 3,000 people, in order to legitimize the war on terrorism.

The Novus poll indicates that a significant number of young Swedes are persuaded by the logic of the argument.

Of the 1,000 Swedes surveyed in an internet panel, 70 percent responded that al-Qaida were behind the attacks, while seven percent did not think so.

Among those under-30 only 58 percent believed responsibility lay with al-Qaida, while 15 percent did not.

When asked whether the US government orchestrated the attacks, eight percent supported the theory while 64 percent rejected it.

However among the under-30s there was once again more scepticism: 51 percent rejected the conspiracy theory while 18 percent believed that the US government, led at the time by President George W Bush, had a role in the attacks.

As many as 31 percent of the young people interviewed in the survey responded that they did not know what to believe.