Europe has long divided the UK's political parties, especially the Conservatives and Labour. The parliamentary vote to enter the Common Market relied on rebel pro-European Labour MPs, while in the 1980s Labour was calling for withdrawal. If a decade on the Conservative Party saw a growing number of rebels against the Treaty of Maastricht, three decades later those Tory rebels — alongside a new party established to oppose membership, the UK Independence Party — have grown in number and look to the UK's ultimate withdrawal from the EU. This article explores the impact of European integration on British party politics, examining the ways in which it has caused division and fragmentation at the national level. It then looks at the impact of British membership on European level parties, which have also seen a degree of fragmentation owing to the nature of British parties.