Brighton and Hove City Council's leader resigned last night only a week after he denied he was about to step down.

Ken Bodfish OBE, who has led the city council for six years, announced his decision to colleagues at a Labour Party meeting in King's House, Grand Avenue, Hove.

He said he was leaving to chair the new Sussex Partnership NHS Trust, which will be responsible for specialist services for mental health, learning disabilities and drug abuse across the county.

In a statement, he said: "I have been proud to be the leader of this city and of the achievements that this council has made.

"I would like to take this opportunity to thank colleagues of all political parties with whom I have worked over the last few years."

He said was also resigning as chairman of the policy and resources committee but would remain a ward councillor for Queen's Park.

His resignation will come into effect from February 1.

In recent months, The Argus has reported of a growing rift between Coun Bodfish and colleagues on the council.

After last night's meeting, Coun Bodfish told The Argus his new post begins on April 1 but he will be working to set up the trust in the meantime. A chief executive is due to be appointed this week.

He said: "It is a new challenge. It is an important challenge.

"Large numbers of families are affected by mental health issues and substance abuse. It is a major issue for the city and the county as a whole."

He said his duties at the council would be carried out by the deputy leader Councillor Sue John until a replacement is appointed.

Mr Bodfish denied his resignation was connected to the difficult times he had faced during the past year, including a vote of no confidence 12 months ago when a debate about council housing was pulled from a public meeting at the last minute.

He said: "I never intended to really continue much beyond 2007.

I think six years as a leader of the city is a reasonable time.

"I am proud of my achievements.

"I think those colleagues who worked with me are sorry there is going to be a change. I think they all recognise the work of the trust is important.

"I am looking for new personal challenges."

Garry Peltzer Dunn, the leader of the Conservative opposition, said: "I am pleased from a personal point of view that he will remain as councillor as I think he has a lot to offer.

"We have all heard stories that his party has become dissatisfied. It may be that this helped him to make this decision. I am sure he made this decision not only for himself but for the benefit of the whole party."

Councillor Keith Taylor, Green Party convenor, said Coun Bodfish's departure for the NHS confirmed that the New Labour project in Brighton and Hove had ground to a halt.

Lib Dem councillor Paul Elgood said: "I wish Ken well. He was a very high profile leader with very strong opinions but certainly now is the time for a fresh approach."

Lib Dem leader David Watkins said last January's vote of no confidence in Coun Bodfish's leadership was the start of a "slippery slope" that probably led to his departure.

He said: "He had a difficult job and whoever takes over will have to ensure they carry not only the party but the rest of the council."

There was speculation that Councillor Simon Burgess was the most likely candidate to take on the role with Coun John or Councillor Gill Mitchell also named as possible contenders.

Labour councillor Gill Mitchell declined to comment further on Coun Bodfish's resignation.

She said: "Obviously, we will be moving ahead with a procedure to elect a new leader of the Labour Group because we need to do that fairly swiftly."