Nick Clegg threatens to derail David Cameron's EU referendum plan ©Getty Nick Clegg, left, and David Cameron: the deputy PM said the tax proposal is 'patronising drivel that belongs to the Edwardian age' Nick Clegg has threatened to derail David Cameron's planned EU referendum in any future coalition government, claiming the Conservatives were "talking to themselves" over Europe. The Liberal Democrat leader on Monday said his party did not support the prime minister's planned referendum in 2017 following a "so-called renegotiation" of Britain's relationship with the EU. The Lib Dems would support such a vote only if there were a new treaty transferring powers from Britain to Brussels. It is not clear whether this would happen. Mr Clegg said the Lib Dems believed there would never be a case for leaving the EU, which he said protected jobs and British influence. "We will always be the party of "in,"" he said. The deputy prime minister's comments came ahead of a Commons vote on Friday on a bill to enshrine the proposed 2017 referendum in law, a measure Mr Cameron hopes will demonstrate the Tories are on the side of public opinion. Mr Cameron is expected to vote in person for the private member's bill introduced by Tory MP James Wharton. But most Labour and Lib Dem MPs will stay away, with both parties claiming the bill is simply a way for Mr Cameron to manage the internal Tory debate about Europe. Mr Clegg and Ed Miliband, Labour leader, believe the measure will eventually die because of a lack of parliamentary time; bills introduced by backbench MPs are susceptible to being "talked out" by opponents. But Mr Cameron hopes the bill will flush out Mr Clegg and Mr Miliband's bottom line on Europe. Speaking during a visit to Afghanistan, Pakistan and Kazakhstan, he said: "I would say to all MPs: turn up and vote." Mr Clegg and Mr Miliband hope to hold to a joint line on a referendum - effectively the position enshrined in the coalition's own 2011 EU Act, which requires a plebiscite if there is a future transfer of power to Brussels. Aides to the Lib Dem leader said that would be the party's manifesto pledge at the next election, although Mr Clegg refused to say whether it would be a "red line" issue in any future coalition negotiations. Mr Miliband's allies have played down suggestions that Labour could try to trump Mr Wharton's bill by pushing for an in-out referendum before the election. Against a backdrop of political manoeuvring on Europe, more than 170 business leaders on Monday called for an immediate start to liberal economic reforms to the EU along lines set out by Mr Cameron. Among those signing in a personal capacity were a number of senior City figures including Sir Win Bischoff, chairman of Lloyds Banking Group, Douglas Flint, chairman of HSBC, and Ian Powell, chairman and senior partner of PwC, the professional services firm. The Business for New Europe manifesto calls for a completion of the single market, free trade agreements, more help for smaller companies, enhancing the role of the City as "the world's financial centre in Europe" and less EU red tape. Speaking at the launch, Vince Cable, Lib Dem business secretary, agreed the reforms were needed now and described talk of a referendum as "a serious distraction."