UK: odds on the euro?

I am told that William Hill are opening a book on whether the UK will join the euro and when. The odds:

During 2009: 20/1
During 2010: 14/1
During 2011: 10/1
After 2014: 2/7

I should have thought the 2010 bet is the best: Labour win the general election and join immediately. But neither scenario looks likely to me. Good luck to the punters.