Q&A on the Damien Green arrest

It is believed to date back more than a year - to November 2007 when a leak suggested that Home Secretary Jacqui Smith covered up a scandal in which 5,000 illegal immigrants were allowed to be licensed as security guards.

Who requested the inquiry?

Jacqui Smith denies it was her or any other minister. Sir David Normington, the Home Office Permanent Secretary, says he called in the Cabinet Office's specialist leaks unit. He let Ms Smith know it was under way. Within two to three weeks the police were called in - but nobody has said if or when Ms Smith was told of this move.

Who else knew?

The head of the Home Civil Service, Sir Gus O'Donnell, told Gordon Brown. It is impossible that Sir Ian Blair, then Scotland Yard Commissioner, did not know.

When were ministers told that the police were involved?

Nobody is saying - but they certainly knew before the raids took place.

What was the first significant move?

It took until last month for an arrest to be made - that of Christopher Galley. The assistant private secretary in the Home Office was previously a Tory election candidate in 2004.

Why was Damien Green's name in the frame?

Mr Green was known to be the source of the stories which had embarrassed Ms Smith - in fact, it was no secret. The arrest of Mr Galley led detectives to conclude that they should arrest Mr Green.

Who gave the arrest and raids the go-ahead?

It was authorised by Assistant Commissioner Bob Quick, head of special operations in Scotland Yard. Sources say Deputy Commissioner Paul Stephenson, was informed but did not overrule him.

What happened next?

Police spoke at least 24 hours before the raids to the Serjeant at Arms, Jill Pay. It is highly unlikely she allowed the police search without telling Speaker Michael Martin. Tories claim she was incorrectly told senior law officers had authorised the move. The Director of Public Prosecutions was informed but is not understood to have given advice or authorisation.

Who else knew about the arrests and raids in advance?

Sir David Normington, David Cameron and Boris Johnson were all told in advance But crucially ministers say they were not.