just saw this episode, and noted in the credits Guest Voice: Tony Blair - sure the PM himself wouldn't do this?
The only simpsons guest characters they haven't had the real-life people do the voice for are politicians like Bill Clinton or George Bush (Snr) (though very good soundalikes!).
and yet they get Prime Minister Blair to do a guest voice? They certainly didn't get HRH Elizabeth II to do HER voice!
Another thing they do a better british accent than australian - for american actors doing cartoon voices..