Figures to substantiate what I wrote in my previous post:

Total votes for Labour in the London Assembly election: 911,204
Total votes for Conservatives in London Assembly election: 708,528

Total first preference votes for Ken Livingstone: 992,273
Total first preference votes for Boris Johnson: 1,054,811

So in fact Ken Livingstone's vote was higher than the vote for Labour in the Assembly election. Just not higher enough.