Yes, Prime Minister S01E03 - Gentleman's Agreement

To begin with, it looks as if Jim has defeated Humphrey's scheme to get Britain into the Euro. But Bernard tells Humphrey he has found evidence of some dodgy expenses claims by Jim when he was in opposition. However, when Humphrey tries to use this lever, he discovers that Claire has unearthed some of his own equally dodgy expenses claims. So they come to a gentlemen's agreement, and Britain is saved from the Euro.