Image copyright PA Image caption Lord Lawson will be president of Conservatives for Britain

A group formed to push for a UK exit from the EU has told a rival Eurosceptic campaign to "shut up" and branded its leader a "has been".

UKIP-backed Leave.EU spoke out after Lord Lawson was confirmed as president of the Conservatives for Britain group.

The ex-chancellor said he acted early to prevent "less moderate, xenophobic voices" dominating the debate.

He said he would not share a platform with Leave.EU but said all were welcome to "rally" to his group.

The Electoral Commission has yet to nominate the official pro- and anti-EU campaigns in the referendum, promised by David Cameron before the end of 2017.

The PM is attempting to reform the UK's relationship with the EU beforehand.

'Rabble'

Lord Lawson said he had accepted the position as president of Conservatives for Britain because he believed it was "far more likely" the government would be unable to secure the reforms it hoped for.

In response, UKIP leader Nigel Farage said Lord Lawson, chancellor from 1983 to 1989, was "intimately associated with the Thatcher years" and this would limit his campaign to Conservative voters.

And in a joint statement, three key figures behind Leave.EU, including its founder, former UKIP donor Arron Banks, said Conservatives for Britain was "run by the Westminster bubble".

"It would be better if the Eurosceptic Tories just 'shut-up' as they are going to alienate the vast majority of people who will look at this campaign as a Tory stitch-up," they said, adding: "If the Tories keep using has-beens like Lord Lawson and the other Eurosceptic rabble then that will turn off supporters."

Conservatives for Britain is led in the House of Commons by MP Steve Baker, and includes former ministers Owen Paterson and John Redwood.

Setting out his pitch in The Times, Lord Lawson wrote: "A number of my colleagues in the Conservative Party are waiting to see what the prime minister negotiates before deciding which way they will vote or whether they will campaign for 'in' or 'out'.

Image copyright EPA Image caption Nigel Farage says his party stands "hand in hand" with Leave.EU, the campaign founded by Arron Banks (right)

"We cannot afford to wait that long. If we leave the playing field vacant, less moderate, xenophobic voices will dominate the debate and we will fail as soon as the government, the major political parties, the CBI and trade unions declare they are backing the 'in' campaign."

Among the demands the government has called for in its renegotiation are more power for national parliaments over EU decisions, restricting the rights of EU migrants to claim some benefits in the UK and an opt out from the ambition of ever-closer union.

Nigel Lawson: Profile

Image copyright PA Image caption Then Prime Minister Margaret Thatcher with Nigel Lawson in 1988

A self-proclaimed Tory radical and long serving chancellor in the 1980s, Nigel Lawson was a key ally of former Prime Minister Margaret Thatcher.

After studying at Oxford University, he embarked on a career in journalism. He joined the Financial Times in 1956 and five years later became City Editor of the new Sunday Telegraph, then editor of The Spectator.

But Nigel Lawson had political ambitions, and after narrowly failing to win election to parliament in 1970 he entered the Commons in 1974 as MP for Blaby in Leicestershire. When Margaret Thatcher won the Conservative leadership in 1975, he became a key architect of Tory economic policy and after the 1979 election was appointed to the Treasury.

It was as chancellor that the then Mr Lawson made his greatest impact with dramatic cuts in income tax rates, a programme of privatisation of several key industries and extensive de-regulation. However, he opposed the poll tax and in 1989 resigned over a split in views with Mrs Thatcher's special adviser, Alan Walters.

Now 83 years old, Lord Lawson sits in the House of Lords. He is the father of food writer and celebrity chef Nigella Lawson and journalist Dominic Lawson.

Speaking on BBC Radio 4's Today programme, he said there was "no economic benefit" to being in the EU. The union could not be changed without treaty change, which "isn't going to be forthcoming" as it requires unanimous agreement of other members states, he said.

Image copyright AFP/Getty Images Image caption David Cameron has previously said the EU would not work unless it could show flexibility

The official campaigns to remain and to leave will benefit from extra resources.

The Electoral Commission says it will choose the campaign which represents "to the greatest extent those campaigning for that outcome".

Earlier this month, Mr Farage said his party would work "hand in hand" with Leave.EU , billed as an "umbrella group" of anti-EU campaigners.

UKIP's only MP, Douglas Carswell, has said his party must be willing to "work with anyone" and has suggested he may back Business for Britain, which has been in discussions with Conservatives for Britain about forming a joint campaign.

The Clacton MP had an angry exchange of views on the matter with Mr Banks at UKIP's conference.

Mr Cameron, Chancellor George Osborne and Foreign Secretary Philip Hammond have all been engaged in diplomatic talks on the UK's relationship with the EU.