LONDON - Prime Minister David Cameron has raised the prospect of a possible referendum on Britain's future relationship with the European Union, potentially threatening trade with the bloc and opening up another front against the Conservatives' coalition partner.

Britain has had a long and painful history of infighting and changes of heart over how closely to integrate with the EU ever since it joined its precursor four decades ago.

It has often proven divisive both within and among Britain's main political parties as well as the public.

Fears over closer fiscal union in the single currency bloc in response to the euro zone debt crisis has heightened concerns among backbenchers, especially among the euroskeptics on the right of the Conservative Party and the electorate.

Polls suggest that if given a chance, voters would opt out of the EU.

Cameron, writing in the Sunday Telegraph, said he believed the "vast majority of the British people," like him, wanted to make changes to Britain's current relationship.

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