What's the point of impeachment in a parliamentary democracy?  You want a PM out in the UK then all you need to do is to either convince a majority of Labour MP's to dump him or enough Labour MP's to join with the Conservatives and LD's to vote for a no-confidence motion.  If you can't do that then you surely can't actually impeach Blair.  The talk of impeachment in Britain over the past year or two seems like a silly side effect of spending too much time thinking about American politics.