Prime Minister Gordon Brown and his government were yesterday forced to deny that they had been involved in the arrest of a senior opposition politician quizzed by detectives over alleged information leaks.

Damian Green, 52, the Conservative Party's immigration spokesman, was detained by London police at his home in Kent on Thursday as part of a probe into leaks of government material by a Home Office official which he then made public.

Mr Green was questioned for nine hours and his offices were searched by counter-terrorism officers.

Conservative leader David Cameron said the unprecedented arrest, and the "heavy-handed" manner in which it was carried out, raised some very serious questions.

"I think these are extraordinary and rather worrying circumstances," he told reporters. "What seems to be the case is that he was arrested for making public information that the government did not want to have made public."

Former Conservative home affairs spokesman David Davis said the action was "somewhere between an astonishing error in judgment through to judicial intimidation" and likened it to draconian action taken by political leaders in Zimbabwe.

The Metropolitan Police said they acted after receiving a complaint from the Cabinet Office - the department charged with enforcing the rules governing the conduct of all government employees and ministers.

Detectives said the decision to detain Mr Green had been made solely by the police. Mr Brown and other senior ministers insisted the Labour government had not played any role.

"I had no prior knowledge, the Home Secretary had no prior knowledge, I know of no other minister who had any prior knowledge," he told Sky News.