Boris Johnson has distanced himself from hardline Tory demands for a straightforward referendum on whether Britain should remain a member of the European Union (EU).
In a move that will help David Cameron resist growing backbench demands for an in/out referendum, the Conservative Mayor of London said the UK's relationship with Brussels should not "boil down to such a simple question".
The Prime Minister has signalled his readiness to hold a referendum on the EU but is opposed to an in/out alternative. He wants to use it to receive "fresh consent" for a renegotiation of Britain's position in the EU.
Influential eurosceptic backbencher Mark Pritchard, a former secretary of the 1922 Committee of Tory MPs, stepped up calls for a referendum on the question of Britain's future membership. He urged ministers to bring forward legislation before the end of the parliament. He said in an article for the Telegraph website: "This should be an in/out referendum - anything short of that simply won't deliver."
Mr Johnson said that any further fiscal integration or banking union should trigger a referendum but that a single question on whether the UK should remain a member state was unnecessary.
Speaking to Pienaar's Politics on BBC Radio Five Live from India, where he is conducting a trade mission, Mr Johnson said: "I certainly think that if there was to be a new treaty for instance on a fiscal union or on a banking union or whatever, then it would be absolutely right to put that to the people.
"Whether you have an in/out referendum now, I can't quite see why it would be necessary. The thing that worries me is that the European Union is basically changing from what it was initially constituted to be. It is becoming the eurozone de facto, and the eurozone is not something that we participate in.
"I think it is becoming a little bit unfair on us to be endlessly belaboured and criticised for being the back-marker when actually we think that this project is not one that is well founded or well thought through.
"It is extremely painful and difficult. If and when the eurozone goes forward in to the way that seems likely in to the banking union, in to a full-scale political union, then I think it is inevitable given the changes that will entail to the European Union that we will have to consult the British people about what they want and in those circumstances yes, we should jolly well have a referendum."
The Mayor, who is influential among many Tory backbenchers sceptical about Mr Cameron, said the prospect of Britain's withdrawal from the EU was unappealing. He said: "Suppose Britain voted tomorrow to come out, in real terms what would happen is that the entire (Foreign Office) delegation would remain in Brussels. We would still have huge numbers of staff trying to monitor what was going on in the community, only we wouldn't be able to sit in the Council of Ministers, we wouldn't have any vote at all."