MIG wrote:

I agree that he might not have won without the backing of Labour in
2004, but then again, his association with Labour in 2008 was probably
a sufficient handicap for him to lose to Boris, although by a far
smaller margin that Labour was losing to Conservatives elsewhere.

I think in 2004 he would probably have won as an independent. Labour had
selected Nicky Gavron as their candidate and rapidly learned that Assembly
Members, even sitting Deputy Mayors, have zero profile and all polls
suggested she would come fourth while Livingstone won. Remember that the
Conservative candidate Steve Norris was also engulfed with some problems in
that election and had the race been considerably closer they would
undoubtedly have got more attention, both putting off voters and also acting
as a damper on Conservative activists' enthusiasm. Never underestimate how
much momentum can be lost if the activist base is unenthusiastic - Labour
similarly did badly in 2000 because many activists didn't want to actively
campaign against Livingstone.

(And before anyone raises the prospect of Simon Hughes coming through the
middle, even before the notorious revelations in 2006, the Liberal Democrats
have always found elections on a London-wide and regional basis very hard to
fight because the battleground is so different from the localised fights
where their successes are. At the local level they combine pavement
politics, parochialism and appeals for tactical votes to get success. But on
a London wide basis they're having to fight on too many fronts to get a
consistent message together and can't just run a campaign based on being in
second place. Their organisation in London is also very patchy - strong in
areas like Hughes's home base of Southwark or the south west boroughs,
partial in some other boroughs and non existant in a few. The voting system
also hurts them badly as it encourages protest votes to scatter across
parties but denies a third placed party the opportunity to harvest transfers
to get into the top two.)