Conservative former Chancellor Lord Lawson has said there is a "clear" case for Britain's withdrawal from the European Union, insisting the economic benefits would "substantially outweigh the costs".
But what do the key players in British business think?
ITV News Economics Editor Richard Edgar reports.
The Mayor of London Boris Johnson has criticised Lord Lawson for not allowing time for the negotiations in Europe to take place.
Speaking on LBC 97.3 radio the Conservative said London needed Europe and access to European markets.
– Boris Johnson, Mayor of London
Myself, I think it would be better to stay in the single market, to have the benefits of a customs union, the benefits of completely untrammelled free trade, rights of establishment all those kinds of things, those are very important for British business.
I think the crucial thing we need to focus on is Britain has a global future, London has a global future, we need to be in Europe, in European markets but we also need to look around the world.
Nick Clegg has told Daybreak that Lord Lawson's call for Britain to leave the European Union shows "the Conservatives are struggling to work out how to deal with UKIP".
The Deputy Prime Minister said the former chancellor's advocated move would weaken the UK.
"We need to reform the European Union but not turn out backs on it because to do so would make us less safe and less prosperous," Mr Clegg said.
"I think that if we were to leave the European Union we'd jeopardise up to three million jobs in this country that are dependent on our place in the world's largest border-less single market," he added.
"We'd make ourselves less safe, because we work in the European Union, to go after criminals who cross borders. It would be more difficult to deal with environmental challenges which cross borders.
"We wouldn't be taken as seriously by the Americans who like the fact that we stand tall in our own European back yard."
A Downing Street spokesman has insisted the government has a "clear timetable for reform" after the former chancellor Lord Lawson declared he would back a campaign to withdraw Britain from the European Union.
Lord Lawson who was a key player in Margaret Thatcher's government, said David Cameron's negotiations would lead to no concrete reform in Brussels.
A spokesman said: "The PM has always been clear: we need a Europe that is more open, more competitive, and more flexible; a Europe that wakes up to the modern world of competition. In short, Europe has to reform."
"But our continued membership must have the consent of the British people, which is why the PM has set out a clear timetable on this issue."
Former Chancellor Lord Lawson has said he believes the gains of leaving the European Union would "substantially outweigh the costs." Writing in The Times, he said:
In my judgement the economic gains would substantially outweigh the costs. The only gain that can be clearly quantified is that we would no longer pay our annual membership fee of some £8 billion. [...]
But there are other, more important gains than this. It is widely recognised throughout Europe that, safely removed from effective democratic accountability, the EU has become a bureaucratic monstrosity. This imposes substantial economic costs on all member states.
Former Chancellor Lord Lawson has said he will be voting to leave the EU in 2017 if he gets the opportunity to do so.
Lord Lawson, who was Margaret Thatcher's longest-serving chancellor and remains a highly-respected figure within the party, also said that it was "by no means assured" that Mr Cameron would win the 2015 general election. He said the economic case for leaving was clear:
You do not need to be within the single market to be able to export to the European Union, as we see from the wide range of goods on our shelves every day. The statistics are eloquent.
Over the past decade, UK exports to the EU have risen in cash terms by some 40%. Over the same period, exports to the EU from those outside it have risen by 75%.
The heart of the matter is that the relevant economic context nowadays is not Europe but globalisation, including global free trade, with the World Trade Organisation as its monitor.
Lord Lawson has called for the UK to leave the European Union. Writing in The Times he described the EU as a "bureaucratic monstrosity" and said the "case for the exit is clear."
The former chancellor of the exchequer said leaving the EU would save the City of London from a "frenzy of regulatory action" and would be a wake-up call for business leaders to the "great opportunities" of the developing world.