The man in charge of MI6 will quit next year, officials have revealed.

Sir Richard Dearlove will stand down in August 2004, the Foreign Office confirmed at the weekend.

Officials denied the decision was linked to the row over the war in Iraq.

Sir Richard, 58 will be leaving the Secret Intelligence Service - the official name for MI6 because he will have been in charge for five years.

This is the normal span for the post of "C" - the code name for MI6's boss. The name is derived from Mansfield Cumming who is credited with setting up the service.

A Foreign Office spokesman rejected media claims that the announcement was linked to the Iraq dossier row.

"Sir Richard Dearlove continues to enjoy the fullest possible confidence of the prime minister, the foreign secretary and the rest of the government on Iraq and all other intelligence issues," said a spokesman.

He was drawn into the row after it was revealed that he had given an off-the-record briefing to the BBC's Today programme.

When Lord Hutton announced his inquiry into the death of Iraq scientist Dr David Kelly, he made clear that he expected to hear from some witnesses behind closed doors and many predict that Sir Richard will be called as a witness.

The Foreign Office took the unusual step of clarifying a departure that in the past would barely have raised a mention in the press.

"Sir Richard Dearlove intends to leave is post as planned in August 2004 on completion of his normal tour of office. This is in no way connected to events relating to Iraq,'' the Foreign Office said.

"In recent times the normal tenure of service as 'C' has been around five years. For example, David Spedding served from 1994 to 1999, Colin McColl from 1988 to 1994, and of their three predecessors no one served longer than five years.''

No details were revealed on who his successor will be though the Observer revealed Sir Richard has broken with convention and appointed a deputy.

Also tipped for the post is former SIS officer and chairman of the Joint Intelligence Committee, John Scarlett.

The man who headed the SIS unit in Moscow and backed the government's Iraq dossier is believed to be the favourite of Downing Street.

The Conservative spokesman on security issues, Patrick Mercer, paid tribute to the spy chief's record.

"Sir Richard Dearlove has been a highly competent and principled MI6 Chief,'' he said.

The party called for reassurances that his replacement would not be closely linked to the prime minister."He will be missed as the war on terrorism proceeds and I trust his successor will follow as independent and analytical line as he has. I very much hope that the new head of MI6 hasn't shared a flat or played in the same band as Tony Blair.''

Liberal Democrat foreign affairs spokesman Menzies Campbell rejected the government's claims, arguing the announcement had been hastened by the events of recent months.

"There is no doubt that there has been considerable tension between the security services and Number 10 Downing Street which dates back long before the present controversy," he said.

"In order to re-establish a proper relationship it is almost certainly necessary for the head of MI6 to go. Sir Richard Dearlove, who has been a distinguished public servant, is taking the honourable way out."