Britain's top intelligence adviser is seriously ill in hospital, the Cabinet Office said yesterday.

Alex Allan, who heads the Joint Intelligence Committee, fell ill on Monday.

Whitehall sources said it was unclear why he collapsed but they did not believe the cause was "foul play".

Scotland Yard said the incident is being treated as "non-suspicious".

A Cabinet Office spokeswoman said: "We can confirm that Alex Allan was taken ill on Monday and transferred to a London hospital.

"We cannot discuss his condition as it is a private matter."

A spokesman for the Metropolitan Police said: "We were made aware of a man in his late 50s who was taken to a London hospital after being taken ill at his home address.

"He remains in a serious condition. This is being treated as non-suspicious."

The 57-year-old's wife, artist Katie Clemson, died from cancer last November.

Mr Allan reported feeling unwell towards the end of last week and remains in a coma while the hospital conducts tests.

The Joint Intelligence Committee (JIC) is part of the Cabinet Office and responsible for briefing the Prime Minister on a weekly basis.

Personnel from MI5, MI6 and GCHQ sit on the committee, and the chairman collates their findings and presents them to the Prime Minister and other senior ministers.

Mr Allan was appointed to the position last November. He was chosen partly because it would be the last appointment of his career.

The rules were changed following the Butler report into the preparation of intelligence assessments.

It was agreed then that the chairmanship of the JIC would be the last appointment a civil servant would hold.

Former JIC head Sir John Scarlett became head of MI6 after the committee's work on the so-called "dodgy dossier" which claimed that Iraq's weapons of mass destruction could be launched within 45 minutes.

Mr Allan began his Whitehall career in 1973 working in anumber of department and for the Cabinet Office.

He has also been high commissioner to Australia, the Government's e-envoy, and he took a break from Government service between 2001 and 2004 to live in Western Australia, where he worked on a range of IT and government issues.

Mr Allan is an untypical civil servant, and his appointment raised eyebrows after it emerged he ran a website for fans of late 60s hippie band The Grateful Dead.

The site lists single and album details as well as fan trivia.

During a rail strike in the 1980s, he windsurfed along the Thames wearing a suit, tie and bowler hat and carrying an umbrella and briefcase.

But, unfortunately for him, he came unstuck when a gust of wind blew him from his board near Big Ben.

A man from the ministries