LONDON - A SENIOR lawmaker from Britain's main opposition Conservative Party was arrested on Thursday amid a probe into leaked information, the party and police said - sparking a furious political row.

Damian Green, the party's spokesman for immigration, was questioned at a London police station before being bailed. He was told to return for questioning in February, police said, but was not charged.

He told reporters after his release that he had 'many times made public information that the government wanted to keep secret - information that the public has a right to know', but insisted he had only been doing his job.

Reports suggest the allegations centre on a number of recent media stories that have caused embarrassment to the government, including the revelation that an illegal immigrant had been employed at the House of Commons as a cleaner.

The Home Office revealed on Thursday that one of its officials was arrested last week 'in connection with an inquiry into alleged leaked documents'.

The Tories said counter-terrorism officers helped search Green's offices at home, in parliament and in his constituency in Ashford, southeast England.

'I emphatically deny I have done anything wrong,' the MP said.

He told reporters: '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.'

Tory finance spokesman George Osborne described the arrest as 'absolutely extraordinary', telling the BBC: 'It has long been the case in our democracy that members of parliament have received information from civil servants.'

Prime Minister Gordon Brown's ruling Labour party denied involvement in the affair, and his office said: 'The prime minister had no prior knowledge of the arrest of Mr Green and was only informed after the event.'

London's Metropolitan police (MPS) also sought to head off any suggestions that the arrest was politically motivated, saying officers acted on a complaint from the government department regulating the civil service.

'The decision to make today's arrest was taken solely by the MPS without any ministerial knowledge or approval,' it said in a statement.

London's Conservative mayor, Boris Johnson, said he was informed of police plans in advance and voiced 'grave' concerns to acting commissioner Paul Stephenson, warning him that he did not regard it as 'common sense policing'.

Announcing the arrest earlier, the Conservatives said: 'We can confirm that Damian Green was arrested earlier today in connection with his work as opposition spokesman for immigration.'

'As shadow immigration minister, Mr Green has, on a number of occasions, legitimately revealed information which the Home Office chose not to make public. Disclosure of this information was manifestly in the public interest.'

Police said in a statement that a 52-year-old man had been arrested in Kent 'on suspicion of conspiring to commit misconduct in a public office and aiding and abetting, counselling or procuring misconduct in a public office.' -- AFP