Lord Winston has stepped back into the fray over NHS funding - challenging Tony Blair to give a firm commitment on massive spending increases.

In an interview on BBC Radio 4's Start the Week, Lord Winston agreed that bringing the UK's spending on health up to the EU average should be a pledge rather than an aspiration.

Prime Minister Tony Blair had appeared to give that commitment the previous weekend, but later stressed that this was only achievable if the economy remained strong.

Asked whether the spending should be a definite pledge and not dependent on the economy, Lord Winston said: "I think that's fair. I think that's a fair comment in a fair society."

Lord Winston's criticisms of the government's handling of the NHS in an earlier New Statesman interview sparked a political row.

His subsequent attempt to retract his comments led to claims that he had been following the orders of Downing Street.

Lord Winston, a fertility expert, denied this, saying: "Nobody's got to me."

He described the UK's current health spend as "ludicrous", dismissing claims that the European health systems consume more money only because they are less efficiently run.

The UK currently spends 6.8% of its gross domestic product (GDP) on healthcare, while the EU average is 8% - although analysts from health charity the King's Fund claim it is 8.6%.

To match this, the UK would have to spend upwards of £11bn - real terms rises of 5% every year for the next five years.

The King's Fund warned that spending on that scale would require cutbacks in other ministerial budgets.

At Prime Minister's Questions last week, Tony Blair told the House of Commons that he "stood by" what he had said on the BBC's Breakfast with Frost the previous weekend.

On that programme, he said that the UK's health spend was "too low" compared to the EU average, adding: "We'll bring it up to there."

When questioned on the timetable, he confirmed the five-year figure.

Mr Blair's official spokesman said later, when asked if the premier would meet Lord Winston: "Robert Winston is somebody for whom the Prime Minister has a very high regard and he's always interested in seeking the views of people who are experts in their field."

On Government policy, the spokesman added: "There is a clear strategy, which is extra resources tied to modernisation and reform.