David Trimble has announced he is quitting as Ulster Unionist Party leader, adding to the problems facing any attempt to restart the peace process.

His decision comes a day after his failure to hold the Upper Bann constituency.

That defeat was the low point in a bad day for the UUP as general election results were announced on Friday.

Trimble's party lost five seats, retaining its grip on just one.

"I am pleased to have had the privilege of leading what I regard as the best and most democratic political grouping in Ulster," said Trimble.

"The party chairman will be arranging for a meeting of the party executive to make the arrangements for a special meeting of the Ulster Unionist Council to elect a new leader at which point I shall formally resign."

The election saw Sinn Fein gain a seat while the Democratic Unionist Party won four more to take its total to nine.

Trimble, who won the Nobel peace prize for his role in securing the Good Friday agreement, said he was "proud of his record".

But the UUP's future looks uncertain following the dramatic switch in support among the unionist community to the DUP.

Trimble may be given a seat in the House of Lords, however.

The loss of the UUP leader and the uncertainty caused by the leadership election the party will now undertake will add to the difficulties facing the peace process.

Sinn Fein's Gerry Adams has called for talks to begin as soon as possible.

But the DUP is set to interpret its victory as indicating support for its tough stance calling for the end of IRA criminality before talks can begin.

The resignation will add to the problems facing new Northern Ireland secretary Peter Hain.

Following his appointment, he said the Good Friday agreement would continue to form the basis of the peace process.

"As the prime minister has made clear, Northern Ireland remains a priority and the Good Friday agreement continues to provide the way forward," he said.

"There remain the two outstanding issues of ending paramilitary activity and criminality, and securing unionist participation in shared government.

"With effort and goodwill on all sides, I have no doubt that these issues can be resolved.

"I am looking forward to working with the political parties and the Irish and American governments. 

"I will be making contact with them over the coming days about how we can make further progress.

"The key challenge to us all is to achieve the full implementation of the Good Friday agreement.

"The agreement is the route to peace, stability and prosperity for all the people of Northern Ireland. They deserve no less."