UK Prime Minister David Cameron said his renegotiation of Britain's ties with the European Union was "bloody hard work" and refused to rule out campaigning for a British exit in a referendum if other EU leaders failed to grant him the concessions he wants, Reuters reports.

As his ruling Conservative Party gathered for its annual meeting, Cameron urged his party to be patient over Britain's relationship with Europe ahead of a vote on membership which he has promised by the end of 2017.

"If I don't get what I want then I rule nothing out," Cameron told BBC television when asked if he was prepared to lead Britain out of the bloc.

"But I am confident we will get what we need," he said in the northern English city of Manchester, where arguments over EU membership have overshadowed domestic announcements such as paid time off for older workers to look after their grandchildren.

Cameron's party has been riven by a conflict over Britain's relationship with Europe that contributed to the downfall of both Margaret Thatcher and John Major, the last two Conservative prime ministers.

When asked if Britain was drifting towards the EU exit, Cameron said: "I am trying to get for Britain the things that we need and obviously once I have got them I will turn around and make the case for staying in a reformed Europe."