Media playback is unsupported on your device Media caption David Cameron: "I welcome the attention that's being placed on this key pledge."

David Cameron has promised to give voters "a proper choice" between staying in a reformed EU and leaving, in a referendum to be held if the Conservatives win the next election.

The comments come after former Tory Chancellor Lord Lawson warned that any renegotiation with Brussels ahead of a vote would be "inconsequential".

He said the UK should quit the EU, with the referendum being moved forward.

But the prime minister said keeping the "status quo" was not an option.

Mr Cameron is facing increased calls to bring forward a promised referendum on EU membership, following the success of the UK Independence Party (UKIP) in last week's local elections in England.

'Good day'

He says he will hold a vote early in the next Parliament, should the Conservatives win an outright majority at the next general election, but only after renegotiating the terms of the UK's relationship with the EU.

The issue once described by the foreign secretary as a ticking bomb is ticking rather louder

However, Lord Lawson said any such deal would be "inconsequential" as "any powers ceded by the member states to the EU are ceded irrevocably".

He said his argument had "nothing to do with being anti-European", adding: "The heart of the matter is that the very nature of the European Union, and of this country's relationship with it, has fundamentally changed after the coming into being of the European monetary union and the creation of the eurozone, of which - quite rightly - we are not a part.

"Not only do our interests increasingly differ from those of the eurozone members but, while never 'at the heart of Europe' (as our political leaders have from time to time foolishly claimed), we are now becoming increasingly marginalised as we are doomed to being consistently outvoted by the eurozone bloc."

Asked whether Lord Lawson's comments had given UKIP a boost, Mr Cameron said: "I think it's been a good day for the pledge that, if re-elected, I will hold to it in a referendum, so that everyone can have not just a voice on everyone's future in Europe, but a vote on our future in Europe,"

He added that he welcomed the attention Lord Lawson had brought to his plans to renegotiate the UK's relations with the EU.

Mr Cameron said: "Now I want to give people a choice not between the status quo and leaving the European Union. I want to give people a proper choice between Britain remaining in a reformed European Union or leaving that European Union.

As it happens, those who run our biggest companies would tend to be horrified at the idea of withdrawal from the EU.

"That's the choice that people will have, that is the choice that people want and there's only one way to get it and that'll be by supporting the Conservatives at the next election."

At the local elections last week, UKIP - which campaigns for the UK to leave the EU - made substantial gains, while the Conservatives lost control of 10 councils.

But Deputy Prime Minister Nick Clegg, whose Liberal Democrats oppose a referendum, said leaving altogether would "make us less safe because we co-operate in the European Union to go after criminal gangs that cross borders".

He said it could put three million jobs at risk, make it difficult to deal with cross-border threats such as climate change, and would also mean Britain was "taken less seriously in Washington, Beijing, Tokyo".

Replying, Lord Lawson told BBC Radio 4's World at One programme: "Well, that's poppycock but I don't think Nick Clegg, who is a charming young man, has ever purported to know anything at all about economics."

Eurosceptic Tory MP Douglas Carswell urged Number 10 to bring forward legislation for a referendum.

He told the BBC's Newsnight programme: "The beauty of an in/out referendum is that Brussels is not just going to have to negotiate with the Whitehall mandarins, not just going to have to negotiate with David Cameron, they are negotiating with the British people.

"Any deal that comes back is going to have to persuade the constituents that elected me that it's worthwhile remaining inside."