LONDON — Prime Minister David Cameron is to make Finance Minister George Osborne his lead negotiator on Europe and speed up his push to win concessions from the EU before a planned referendum on Britain's membership of the bloc, a newspaper reported. The Sunday Times said Osborne would be backed by Foreign Secretary Philip Hammond. Cameron will send them to Berlin and Brussels as part of a 100-day plan after winning a parliamentary majority on Thursday. Cameron will also prioritize a reform of the country's electoral districts, the newspaper said. Cameron promised voters he would push to reclaim powers from the European Union before holding an in-out referendum by the end of 2017. Much of the plan remains vague but he has said he wants to make it harder for newly arrived migrants to claim welfare benefits. European leaders lost no time on Friday in offering Cameron talks on EU reform, bidding to ease uncertainty about Britain's future in the bloc. The Sunday Times said the changes to electoral districts being considered by Cameron could give his Conservative party an extra 20 seats in Parliament. They hold 331 of the total 650 seats after Thursday's election. Cameron is under pressure from within his party to push for big changes to Britain's membership of the EU and some Conservative lawmakers favor an EU exit. The UK Independence Party (UKIP), which wants Britain out of the EU, won nearly 13 percent of the vote in the election, although it has only one seat in Parliament. An opinion poll published earlier this month showed 34 percent of Britons would definitely vote to remain in the EU, and a further 18 percent would probably vote to stay in. Eighteen percent said they definitely wanted to leave the bloc and 14 percent said they would probably vote to exit. — Reuters