BORIS Johnson upped the pressure on David Cameron by demanding he negotiate a looser relationship with Europe – and hold a referendum on the new deal.

The London Mayor said Britain should exploit the eurozone crisis to free itself from key areas of the European Union, including fisheries policy, social policy and farming subsidies.

Mr Johnson risked angering Downing Street by pre-empting a speech by the PM on the issue and criticising his support for closer eurozone integration.

He rebuffed suggestions from some Tory backbenchers for an immediate vote on membership.

But he said Britain should strip back its participation in Europe.

Mr Johnson predicted the PM would commit to a referendum in a keynote speech on the issue this month.