Eurosceptic Conservative backbencher Peter Bone has welcomed Liam Fox's comments, which he said showed the process of obtaining a referendum on the EU was "gaining momentum at enormous speed"
Mr Bone told Sky News:
I think people are coming round to the idea that we should have a referendum in the next parliament, but we should legislate now, in this parliament, for that referendum, so that no party leader could wriggle out of it.
A lot of people think that the next government should renegotiate the terms with Brussels so we just have an economic relationship, and then put that to the British people - either we accept the new terms or we leave.
I think that's what many, many Conservatives now think should be done and what we would like the Prime Minister to say very clearly.
Former defence secretary Liam Fox has said that the UK should leave the European Union unless there is a rebalancing of their relationship.
Foreign Secretary Hague said there would be a "very, very powerful" case for a referendum if Europe moved towards a more federal system.