Britain’s Conservatives have climbed down from a pledge to hold a referendum on the Lisbon treaty. Leader David Cameron says he can not now because it is effectively EU law, after the Czechs completed the European Union’s ratification process.But he promised to seek the return of some powers to Britain: “There is more we can do than simply promise a referendum lock on any future handover of power. Take the sovereignty of our laws. Because we have no written constitution, unlike many other European countries, we have no explicit legal guarantee that the last word on our laws stays in Britain. There is, therefore, a danger that over time our courts might come to regard ultimate authority as resting with the European Union.” Cameron said that if his party beat Labour out of power in elections next year he would change British law to require a referendum before devolving powers to the EU in the future. He called the Labour government’s failure to have held a referendum on Lisbon a “breach of trust”, and vowed that the Conservatives would make sure that the British people remember who “broke their promise”.