Ken Livingstone tells BBC News Online: "I will fight to make sure Londoners get their choice"

Mr Livingstone's defiant appeal to grassroots members came as a BBC survey revealed the depth of the support enjoyed by a man some ministers want to see at the bottom of the Thames.

Mr Livingstone told BBC News Online that if he is not included on the official shortlist to become Labour's mayoral candidate he will begin an American-style "write-in" campaign, calling on the party's 70,000 members in London to add his name to their ballot papers.

The survey by the BBC's Research Unit found 29 of 42 constituency secretaries around London said Mr Livingstone should be allowed on to the shortlist with only three people saying he should not.

Of those who gave an opinion on who would be the best candidate for mayor, Mr Livingstone polled 18 votes, Euro-MP and leader of the Socialst Group of MEPs Pauline Green received five, and Transport Minster Glenda Jackson won the backing of just three secretaries.

Write-in campaign

The ex-Greater London Council leader's latest tactic follows the decision by the London Labour Party to vet candidates before drawing up a shortlist.

He told BBC News Online: "The Labour Party needs to know I will organise a write-in campaign if I'm kept off the ballot paper.

"Ordinary party members will be able to write my name in. If I can get the majority of the votes that way I think it would be impossible to bar me as a candidate."

He vowed to continue his battle until the day Labour's candidate for mayor was announced.

Dennis Canavan: Standing against his party

But Mr Livingstone said he would not stand as an independent against Labour for the position.

He said: "At the end of the day Londoners have got the right to make the choice and I'm going to fight the damnedest I can to make sure they get what they want."

Earlier, the defiant MP condemned the selection process which could bar him from the contest.

He said: "Where you've got 10 constituencies in London who've put someone forward and they're kept off the panel that will cause bad feeling."

Prime Minister Tony Blair's official spokesman said the vetting procedure in place for London mayor had already been used in Scotland.

"Labour suffered for years in opposition from lack of discipline," he said.

But Mr Livingstone said in Scotland the process had caused Labour MP for Falkirk West Dennis Canavan to stand against his party in the Scottish Parliament elections in May.

'Problems and dissension'

Mr Livingstone said: "It has caused problems and dissension throughout the party wherever it has been applied."

The process selected on Tuesday flies in the face of recommendations set out in the summer by a conference of the Greater London Labour Party, which recommended any candidate with the backing of 10 constituencies should automatically appear on the party's shortlist.

Ken Livingstone and Jim Fitzpatrick debate Labour's selection process

But Jim Fitzpatrick, chair of the London Labour Party and MP for Poplar and Canning Town, said it was arrogant for anyone to think they should automatically right to run as a candidate.

He said the board had merely brought the selection process for mayor of London candidates into line with the process used in other selections.

The final decision on which selection process to adopt rests with Labour's national executive.