The Brent East MP told friends yesterday he will run under his own colours if Frank Dobson, his main rival, defeats him but fails to win majority support among Labour's 60,000 members in London.
Under his plan, Mr Livingstone would also run a slate of independent candidates for the 25-member Greater London Assembly, to be elected at the same time as the mayor next May. He is confident of attracting a wide-ranging coalition including Conservative-leaning business people, environmentalists and apolitical figures. He believes his group could win four or five seats, possibly enough to hold the balance of power with the Greens.
The plan will send shockwaves through the Labour leadership, which hoped it had headed off the threat of an independent challenge by allowing him on to the shortlist last month. Opinion polls suggest Mr Livingstone would defeat both Mr Dobson and the Tories.He has been buoyed by the public support for his campaign, which has received donations from 3,000 people.
Under the electoral college which will choose Labour's candidate, it would be possible for Mr Dobson to win by relying heavily on his overwhelming support among MPs, Euro MPs and assembly candidates. They command a third of the votes, as do trade unions and party members.
Mr Livingstone won a place on the shortlist after two protracted appearances before a Labour Party panel last month. He promised to implement Labour's manifesto and not to stand as an independent. However, some party officials remained convinced he would run under his own steam if he did not win the nomination. They pointed to campaign material using the slogan "Vote London" rather than "Vote Labour".
In public, Mr Livingstone is expected to deny any plans to stand until Labour's candidate is chosen in February. Yesterday he told BBC Radio 4: "I accept the result. There is no question about that. We are all fighting to win, but we'll all support the Labour candidate when they win."
The battle became increasingly bitter yesterday, when Mr Dobson accused Mr Livingstone of "peddling" false rumours that he was depressed.
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