The sacked Bristol professor at the centre of a row over drugs has revealed the Prime Minister repeatedly ignored scientific advice as he laid bare the behind-the-scenes wranglings that led to him being dismissed.

David Nutt was forced to quit his role as the country's top drugs advisor after clashing with the government over its policy on cannabis.

He has now told the powerful committee of MPs that launched an investigation into the sacking that Gordon Brown was formally warned to stop railing against the advice of the Advisory Council on the Misuse of Drugs (ACMD) he chaired, which was made up from the UK's most respected academics.

Mr Brown made untrue statements that skunk, a form of cannabis, was lethal and was the first Prime Minister to dismiss the panel's findings since the Misuse of Drugs Act was introduced in 1971, he added.

In evidence submitted to the parliamentary probe, Prof Nutt said: "Soon after Mr Brown became Prime Minister, he publicly stated that he thought cannabis should be a class B drug as the new form skunk was 'lethal'. This statement is scientifically incorrect and was made without consulting the ACMD.

"The chair explained to him the statutory requirement for him to consult us on such matters and he agreed we could review cannabis again. During this third review there were repeated briefings from the Cabinet Office to the effect that whatever the ACMD decided the PM had determined it would be class B.

"This interference with the due process caused considerable frustration to the ACMD and the then chair Sir Michael Rawlins wrote to the PM to say that if this discourteous behaviour did not stop, the ACMD would cease its review.

"However, despite the ACMD concluding that cannabis was still a class C drug, the Government went against this advice."