British public support to remain in the European Union is at its highest level in 24 years, a poll showed on Friday, as Eurosceptic lawmakers from three parties formed a new group ready to campaign for an EU exit.

The poll by Ipsos MORI showed 66 percent of Britons would vote to stay in the bloc and was released ahead of an EU summit in Brussels next week at which Prime Minister David Cameron will set out plans to reshape his country's EU ties.

Cameron, who was in Slovakia on Friday where he lobbied his Czech and Slovak counterparts on the subject, has pledged to hold an in-out EU membership referendum by the end of 2017 and has said he is confident of securing concessions that will allow Britain to stay in a reformed EU.

Friday's poll asked respondents the same question that will be put to voters in the planned referendum -- 'Should the United Kingdom remain a member of theEuropean Union?'

Ipsos said 66 percent of the 1,005 adults asked said 'yes', 22 percent 'no', and 12 percent said they didn't know. In 1975, the last time Britain held such a referendum, just over two thirds of voters opted to stay in the then European Economic Community.

Ipsos said the last time public support for EU membership was higher was 24 years ago, in 1991, before the Maastricht Treaty renamed the European Community a "union".

"Support for staying in the EU has been growing since well before the (May) election, and now stands at a 24-year high, even if some would also prefer a less political union," said Gideon Skinner, head of political research at the pollster.

"However, Europe is rarely seen as a top priority for voters, and at the time of the 2011 Euro zone crisis the 'outs' were in the lead, so another crisis could see attitudes change again."

But the new poll showed that most Britons (57 percent) were not confident Cameron would be able to renegotiate a good deal for Britain.

The survey came as lawmakers from Cameron's Conservatives and the opposition Labour Party joined the UK Independence Party's sole member of parliament to form a new cross-party group ready to help campaign to take Britain out of the EU.

Separately, Alan Johnson, a veteran former cabinet minister, said he would head up a new Labour Party pro-EU campaign group.