Early reaction to Frank Dobson's election as Labour's mayoral candidate suggests the party may still face problems.

The result means Tony Blair has his favoured candidate as the party's representative for the post as mayor of London.

But he must now turn his attentions to ensuring rank-and-file party members back the official candidate when the election takes place in May.

Speaking to the BBC, Diane Abbott, Labour MP for Hackney North and Stoke Newington, said Mr Dobson's position was unsustainable.

"Ken Livingstone has won twice as many union votes as Frank Dobson and has the support of twice as many Labour members.

"Because of the quirks of the electoral college Frank Dobson has emerged as our candidate.

"But I don't believe Frank's position is sustainable.

"He must consider his position. The world now knows that despite the Labour Party throwing everything against Ken except the kitchen sink that he was able to win every single ballot of rank-and-file members.

"The only people who didn't vote for him were MPs and we did not have a secret ballot and were under a great deal of pressure."

The announcement of Mr Dobson's success received mixed reaction from union representatives.

Sir Ken Jackson, General Secretary of the Amalgamated Engineering and Electrical Union, whose union was strongly criticised by chief rival Ken Livingstone for not holding a ballot of its members, welcomed the result.

He said: "Frank has a long track record of representing ordinary, working people and we supported him because he is in touch with everyone from the grassroots to government."

However, the London convenor for Unison, Geoff Martin, said it was the worst possible result for the London Labour Party, and a dream result for Tory candidate Steve Norris.

He added: "It would be an absolute disaster if Millbank just continued to plough on regardless and ignored the clear wishes of the vast majority of rank-and-file trade unionists and party members who have given such a clear and ringing endorsement to Ken Livingstone."

Despite Mr Martin's comments, Unison put out an official statement calling for Mr Livingstone not to stand as an independent.

Unison spokesman Chis Humphreys said: "We are warning Ken that he should not stand as as independent and if he does, he must expect to not have the support of Unison."

Mr Dobson's Tory rival for mayor, Steven Norris, said the process had been "thoroughly shameful from start to finish".

He said: "No wonder Ken Livingstone is furious - an old socialist, finally defeated by an electoral system that would not be out of place in North Korea.

"From now until polling day, Frank Dobson, who clearly doesn't want the job anyway, will not be able to dodge the charge that not only is he the prime minister's poodle, he is also the candidate his own party didn't want."

Meanwhile Susan Kramer, the Liberal Democrat candidate, who was the first runner to be nominated last August, welcomed Mr Dobson to the race.

She said: "Frank Dobson did not win the majority votes of Labour members and I don't think he will win the majority of Londoners to be honest.

"If Ken is to be believed we have an on-going civil war within Labour."

She said she would also welcome Mr Livingstone to the race should he decide to stand as an independent.