Just because today we look quite good compared with other countries, that's not the basis on which to take a decision as to the future.

Sir Leon Brittan

"Over a period of time... others will benefit in a way that we won't, and therefore our very dominant position at the moment will be gradually eroded," Sir Leon said.

"There are other parts of the British economy which will suffer much more - inward investment is one."

Long term

Sir Leon compared the controversy over euro adoption to the structural and economic reforms put in place by Margaret Thatcher's Conservative government, of which he was a member:

"If you ask me why we are in such good shape now, I would say that it is the benefit that we are getting from the structural changes that... Margaret Thatcher's government actually introduced."

He said we should view the long term future of euro adoption in the same way.

"If you believe that similarly there are structural benefits to be got in the form of the European economy, removing barriers, increasing activity, increasing wealth, increasing trade, increasing investment, then those take time to come," Sir Leon said.

"Just because today we look quite good compared with other countries, that's not the basis on which to take a decision as to the future."

Anti-euro feeling

But Sir Leon said he did not believe it would be easy to turn around widespread public opposition in the UK to scrapping the pound:

"There is a mountain to climb as the result of years of anti-propaganda, aided by some of the most important British newspapers."

The introduction of the euro went smoothly

However he deemed the turnaround as possible:

"I believe that it will be possible - not easy, but possible - to persuade the people of this country who will have to decide irrespective of what party they are, that it is in Britain's interest that we should join."

He has advised Prime Minister Tony Blair to start a "gradual escalation of the rhetoric on the euro", he said, making it clear to Britons what the benefits of joining the euro were.

Long career

Sir Leon Brittan, Britain's longest serving European commissioner, explained in the interview the origins of the Conservative Party's anti-euro stance:

Sir Leon Brittan - profile

1962: Called to Bar, Inner Temple 1974-83: MP for Cleveland and Whitby 1979-81: Minister of State, Home Office 1983-88: MP for Richmond, North Yorkshire 1985-86: Trade and Industry Secretary 1989-93, 95-99: Vice-president, European Commission 1993-99: European commissioner, responsible for external economic affairs and trade policy

"Basically what has happened is that first of all the anti-Europeans, the eurosceptics were very much a minority.

"But because the Conservative government of the day didn't have an overall majority in the House [of Commons], it didn't confront them because these people were quite prepared to bring the government down."

The current Conservative leader, Iain Duncan Smith "made his reputation" opposing the government of John Major, Sir Leon said.

"So it was a very difficult position, and rightly or wrongly, I happen to think wrongly, the government didn't confront the euro sceptics.

"First of all the tail started wagging the dog, and then the tail became the dog."

You can hear the HARDtalk interview in full at the following times:

BBC News 24
23 January 0430GMT, repeated 2230 GMT

BBC World
23 January 0430GMT, repeated 1130GMT, 1630GMT, 1930GMT, 0030GMT.