Former shadow home secretary David Davis has suggested that the arrest of a Conservative frontbench spokesman was reminiscent of Robert Mugabe's Zimbabwe.
Davis told the BBC on Friday that the arrest of immigration spokesman Damian Green was somewhere between "an astonishing error of judgment" and "judicial intimidation".
The Conservative MP also said that the assertion that the prime minister had no prior knowledge of the arrest was "extraordinary".
Green was held in custody for nine hours last night as part of a Scotland Yard investigation into leaked Home Office documents.
Conservative Party leader David Cameron also suggested that "serious questions" needed answering over the arrest.
He said: "I think there are some serious questions that have to be answered. If they wanted to talk to Damian Green, why not pick up the telephone and ask to talk to him?"
It is believed that at least nine counter-terrorism officers were deployed to detain Green and search his house and Commons office on Thursday.
Green, MP for Ashford, expressed his anger in the early hours of the morning at being questioned over a series of confidential Home Office papers.
Speaking outside the House of Commons after being released on unconditional bail at just past midnight, Green said: "I was astonished to have spent more than nine hours today under arrest for doing my job.
"I emphatically deny I have done anything wrong."
He added: "I have many times made public information that the government wanted to keep secret - information that the public has a right to know.
"In a democracy, opposition politicians have a duty to hold the government to account. I was elected to the House of Commons precisely to do that and I certainly intend to continue doing so."
Downing Street and the Labour Party HQ released statements strongly denying that either prime minister Gordon Brown or other ministers had prior knowledge of the arrest.
The Metropolitan Police Service also commented that the decision to take Green in for questioning was taken "solely by the MPS without any ministerial knowledge or approval".
But mayor of London Boris Johnson said he was told of police plans in advance and voiced "grave" concerns to acting Met commissioner Sir Paul Stephenson, warning him that he did not regard it as "commonsense policing".
And Davis insisted that Green was just doing his job.
He told the BBC: "He was holding the government to account on each of the issues that we think the police were interested to hear, he was bringing to the public eye things that the government, in some cases, was actively trying to keep out of the public eye."
"None of this put, in any way, national intelligence, national security or international relations at risk.
"Yet we end up with a circumstance that is reminiscent of Robert Mugabe’s Zimbabwe, with an opposition spokesman being arrested for nine hours," Davis stated.
He claimed that because both Cameron and Johnson had been informed before the arrest took place, it was "astonishing" that no one in senior government knew.
He argued: "I cannot believe it because the simple truth is that… the Home Office initiated this. I am sure the civil servants signed the form but the Home Office initiated the initial investigation.
"Why were they not told? You tell the opposition but you don't tell them? It is extraordinary."
Davis also suggested that the decision to use at least nine counter terrorism police officers for the arrest was overkill.
"The police make judgements every day about what are appropriate resources," the Conservative MP said.
"On a day when I assume our security state must be quite high after the Mumbai atrocities is an extraordinary decision."
Davis claimed that the move was designed to intimidate whistleblowers across Whitehall.
He stated: "You don't need to arrest him. He isn't going to leave the country. Why don't you just go and question him? Why this heavy handed, almost intimidatory approach to it?
"What we are seeing here is something designed to intimidate whistleblowers across Whitehall and actually to undermine the role of opposition doing its job, and doing its job properly in the public interest."
Dods Parliamentary Communications Ltd