A member of the Advisory Council on the Misuse of Drugs has resigned in protest at the government's treatment of its head, who was forced to step down last week after saying that cannabis was less harmful than alcohol or nicotine.
Professor David Nutt's comments – which included the claim that cannabis had been upgraded to class B against scientific evidence for political reasons – led the home secretary to call on him to resign.
Today, Dr Les King told the BBC he had decided to step down because he felt Alan Johnson had denied Nutt's "freedom of expression".
He said that while the government had "a right" to reject the panel's advice, its attitude towards the advisory body had changed "very recently".
King, who emailed his resignation to the Home Office yesterday, added: "I suppose it goes back to 2002 with [then home secretary] David Blunkett who was minded to reclassify cannabis downwards.
"He made it clear to us his wishes. The council supported that.
"In that situation it was something that the council readily agreed to. That wasn't too worrisome but that precedent then continued."
There were reports this afternoon that a second member of the council, Marion Walker, had also resigned in protest at Johnson's treatment of Nutt. However, the Home Office was unable to confirm or deny the reports.
Johnson said today that while he respected Nutt's views, the adviser had "crossed the line".
Speaking to Sky News, the home secretary said: "You cannot have a chief adviser at the same time stepping into the public field and campaigning against government decisions. You can do one or the other, you can't do both."
Johnson said it was not the job of scientific advisers to "just keep coming back and back and back" to overturn ministerial decisions.
He said the decision to force Nutt out had been his alone and he had not consulted Gordon Brown.
He said: "I've got enormous respect for the advisory council. I want to meet them very soon. I've got enormous respect for the scientific community. They've got to understand that Professor Nutt crossed this line between offering advice ... and then campaigning against the government on political decisions."
Johnson said he hoped other council members would not resign.
However, according to today's Observer, several members have sought urgent reassurances from the government that it will not try to control their agenda and will allow them to speak out before they decide whether to quit.
A Home Office spokesman confirmed today that King's resignation had been received, but would not discuss the matter.
"We can confirm that Dr Les King has resigned," he said. "We are not going to give a running commentary on the speculation around further resignations."