The votes cast in total for the mayor and the top up are very similar.
In 2012 it has been well reported that there was only a small Ken drag, however there was a Boris boost. Whilst the Ken drag was 21,286 that he was behind his party, the Boris boost was a massive 262,863!
Looking at 2008, both Ken and Boris ran ahead of their parties. The Ken boost was 228,434 and the Boris boost was 208, 226
Intriguingly in 2004, there was a Ken boost for Labour of 217, 301 but Stephen Norris the Conservative candidate only ran 8,727 ahead of the Conservative top-up vote.
So in 2012 the Boris boost grew by 30% and the Ken boost disappeared.
In the London top up figures there was also a major swing to Labour and a further collapse of the Liberal vote...
2012: LAB 41% - CON 32% - LIB 7%
2008: LAB 28% - CON 35% - LIB 11%
2004: LAB 25% - CON 28% - LIB 17%