David Nutt, the scientist sacked as a government adviser by the home secretary, today defiantly launched his own independent committee which he says will provide the definitive scientific verdict on the risks of drugs.

Nutt said his committee was willing to give advice to the government's Advisory Council on the Misuse of Drugs (ACMD), from which he was sacked as chair.

He was dismissed from the post after criticising politicians for distorting research evidence and claiming alcohol and tobacco were more harmful than some illegal drugs, including LSD, ecstasy and cannabis.

The new committee – called the Independent Scientific Committee on Drugs (ISCD) – includes a number of big names in the field and has the potential to embarrass the government, due to its determination to make public the evidence on the relative risks and harms of drugs without regard to political sensitivities.

Nutt portrayed the ACMD as something of a lame duck scientifically, following the resignations of five of its members in sympathy with him – four of whom have joined the ISCD. "It is a body made up of drug treatment people, police and magistrates," he said.

But the ACMD's new interim chair, Les Iversen, who was appointed this week, had sent him "a very supportive email", he said, "saying he welcomed the committee and hopes we can work together".

The committee will pursue a similar agenda to that which Nutt was sacked for supporting. "We will undoubtedly pull together an assessment of the science, which is likely to challenge some of the aberrations in the current act," he said.

"There's a lot of evidence that MDMA (ecstasy) and related compounds are not class A [the most potentially dangerous drugs]. There's the evidence we presented that cannabis should stay as class C – I think most people would support that. Possibly the psychedelics are inappropriately positioned in class A. And ketamine may be more dangerous than amphetamines – maybe it shouldn't be class C," he said.

The ISCD is currently 14-strong, and includes some very senior names in the field. With Nutt at the launch were Dr Les King, who had a 30-year career in the forensic science service, and Dr John Marsden of the Institute of Psychiatry, both of whom resigned from the ACMD, and Prof Val Curran, a psychopharmacologist from University College London.

It has funding for the next three years from a hedge fund manager, Toby Jackson, who "wants to give something back", said Nutt. In the long-term they hope for more donations and even contracts from the government to carry out scientific research. "It will save them money," Nutt said.

The committee has had its first meeting and decided on a plan of work. Apart from assessing the relative harms of well-known drugs, it will look at the risks of new psychoactive substances – or "legal highs" – which can be obtained through websites, and it will focus on ketamine – also known as K or Special K – which is popular with university students.

Curran said there was concern about the effects on the bladder of frequent use, which had led to young people requiring transplants.

Nutt and Marsden said they felt more comfortable on their independent committee, where they can speak out freely, than on the ACMD. They had been advocating an independent scientific advisory body – which the Dutch have – since 2005, they said.

In a statement the Home Office left open the option for the ACMD to take scientific advice from Nutt's committee.

"The Advisory Council on the Misuse of Drugs is a statutory body, advising the government on drug related issues. Its functions are set out in the Misuse of Drugs Act 1971 and there are no plans to change that," it said.

"When reviewing drugs ... the ACMD routinely considers evidence and reports from a wide range of sources, including external experts. The ACMD will continue to do so to ensure all its recommendations are based on the most up to date evidence."