The MP for Brent East is one of Labour's best-known backbenchers and the front-runner to become the new mayor of London - if party chiefs let him enter the race as Labour's candidate.

Leader of the Greater London Council in the 1980s until Margaret Thatcher's government abolished it, he is considered a fully paid-up member of Labour's awkward squad.

But to Tony Blair's chagrin, though Mr Livingstone may be something of a rebel, he is a popular rebel - he beat Peter Mandelson to a seat on the party's National Executive Committee last year.