Beware that Cameron arguing for a smaller parliament will entrench the two party system with lots of safe seats. If the HofC was cut to 400 and seat to a well over 100,000 it would be desperately difficult for anyone other than the Lab and Cons to win seats. Little chance for Independents/Greens and even Lib Dems would be pushed.
Have a smaller parliament if you wish but it must be by PR and preferably by a system where the electorate and not the party machines decides between candidates from the same party. That system is called STV