Senior Angela Merkel allies warn David Cameron not to "blackmail" EU Allies of the German Chancellor Angela Merkel have warned David Cameron not to "blackmail" Europe by threatening to take Britain out of the EU. The Prime Minister is expected later this month to promise a referendum on a "new settlement" for Britain with the EU - but not until after the 2015 general election. Although he wants the UK to remain a member, there are growing fears among pro-European politicians that a "No" vote in the referendum could result in its departure from the EU. Gunther Krichbaum, the chair of Germany's European affairs committee who is leading a group of senior German politicians on a visit to London, said a British exit would be a disaster for Britain and Europe, and that an attempt renegotiate the UK's membership terms would open a "Pandora's box." There is certainly a risk that [a referendum] could paralyse efforts for a better Europe and deeper integration. Britain would risk being isolated. That cannot be in Britain's interests," warned Mr Krichbaum, who represents Mrs Merkel's Christian Democrats. Asked whether Mr Cameron could win concessions by blocking integration designed to safeguard the euro, Mr Krichbaum said: "You cannot create a political future if you are blackmailing other states. That will not help Britain. It needs a Europe that is stable. It needs markets that are functioning. The Barack Obama administration warned on Wednesday that Mr Cameron could risk undermining British influence on the world stage by putting its EU membership in jeopardy. The Deputy Prime Minister Nick Clegg warned Mr Cameron yesterday that Britain could be reduced to "subsidiary status" if he goes ahead with a referendum which could pave the way for its exit from the European Union. Mr Clegg said: "Whatever question you put in any eventual referendum, the underlying question is the same - does Britain want to lead in Europe and continue to lead... Do we lead or do we hang back in a sort of subsidiary status? Not only ourselves but the Americans and others quite understandably say you are a big nation, you've got big horizons, you've got big ambitions, you've got a big history, act big, don't act small. The Deputy Prime Minister said British leadership in the EU was "an expression of self-confidence." Insisting that he is "not frightened" of a referendum, Mr Clegg pointed to growing doubts on the continent about whether there would be a new EU treaty to entrench eurozone integration. Mr Cameron intends to demand that some powers are returned from Brussels to London during negotiations on such a treaty.