It doesn't matter who is prime minister, the government is always in power.
I think the quote is something like that, which is a slight at the UK civil service because even if you elect a different party, prime minister and ministers control is ultimately held by those who exercise it... which tends to be the civil service.
Another quote along those lines is this one:
Hacker: If there were a conflict of interests which side would the civil service really be on?
Bernard: The winning side, Prime Minister.
Another quote along those lines is this one: