Prime Minister David Cameron lost a symbolically important vote on Europe in the British parliament last week. It’s another setback for the U.K.’s perpetually strained relationship with the European Union and a sign of mounting discontent with European governance. The EU’s leaders should start heeding such signals instead of ignoring them. Unfortunately, British discontent with Europe is easy to ignore because, forgive the expression, it’s such a devalued currency. So when Tory rebels joined Labour to embarrass Cameron by demanding a cut in the U.K.’s contribution to the EU budget, nobody was surprised.