From what I remember due to the figures if he'd gone with Labour it would have been a massively rainbow coalition. I think he got conned by the superior sliming skills of some of the tories and saw a bit of power, then messed up. He went all out to try for proportional representation giving up all other policies and then the tories were able to market that as looking so bad or just uninteresting that the majority either didn't understand the vote or didn't care, so it lost.