Mr Prodi warns of decreased influence outside the eurozone

The European Commission's president also warned that EU members staying outside the eurozone would lose influence over decision-making.

Commons leader Peter Hain had previously said any decision on calling a referendum over British entry would be based only on the UK's economic interests.

Sweden voted decisively to reject the euro in a referendum on Sunday night, held days after the killing of Foreign Minister Anna Lindh.

The final result shows 56.1% voting against the euro, with only 41.8 in favour, on a turnout of 81.2%.

Observers had suggested a 'Yes' vote in Sweden might encourage UK Prime Minister Tony Blair to call a referendum.

Opponents' welcome

Opponents of British entry into the European single currency have welcomed the Swedish result.

Sweden, Britain and Denmark are the only European Union members not to have adopted the currency.

Mr Prodi told the BBC: "We are working to reinforce our institutions, our bank, of course we need to have a more coherent economic policy... if you are not in you are out, it's very simple - you cannot be in and out together."

Asked if he believed the UK would join the euro he said: "No, not now."

Mr Hain said the government still believed it was in Britain's interests to adopt the euro.

The developments over the course of the last 12 months maybe have pushed back the date for a British referendum, maybe into the next Parliament Neil Kinnock European commissioner Sweden rejects euro

Chancellor Gordon Brown had set out a "very clear route map" for British entry, he added.

Mr Hain said Mr Brown's statement, in which he promised to reconsider the question in next year's Budget, had showed there was some way to go on having "flexibility and convergence" to ensure the British economy would go "from strength to strength inside the euro".

Mr Hain added that Britain was "massively down in our share of inward investment compared to the eurozone countries since the euro was established" because investors from Japan and elsewhere found it easier to go into the eurozone.

'Economic mess'

But Lord Lamont, a former Chancellor of the Exchequer, urged Tony Blair not to hold a referendum on the euro in Britain.

"Tony Blair should draw the lesson and should shelve all plans for a referendum in Britain. The Swedes saw clearly the economic mess the eurozone has become," he said.

Shadow foreign secretary Michael Ancram said Sweden's decision served to bolster concerns over joining the currency.

"It strengthens our view that for us to oppose the euro for the UK is right," he said.

Pro-euro European commissioner Neil Kinnock said the Swedish vote was a blow to the commission's hopes, although there had always been a "very substantial gap" between the 'yes' and 'no' votes.

The commission was trying to do more to provide clear public information about the euro, he said, but it was really for national governments to make the pro-euro case.

Mr Kinnock has previously suggested there could be a British referendum in late 2005.

'Advantage'

He told BBC Radio 4's Today programme on Monday: "I think the developments over the course of the last 12 months maybe have pushed back the date, maybe into the next Parliament."

Liberal Democrat Treasury spokesman Matthew Taylor blamed world economics for the downbeat attitude towards joining the euro, and said its attractiveness would grow.

"As Europe comes out of recession, people will see the advantage of the euro, illustrated by the collapse of inward investment in the UK since we opted out," he said.