Ten former British ministers wrote to members of the cabinet yesterday to urge them to push for a referendum on the euro in this parliament, saying the country's success as a trading nation was on the line.

Citing a new study that says Britain's trade would have been £12 billion (€16.7 billion) higher in 2001 had it joined the euro at its inception, the former ministers argued that economic growth, tax revenues and jobs would get a boost from the single currency.

The study and the letter come a week before Mr Tony Blair's government is due to give its long-awaited assessment on euro entry, its most important political decision for a generation.

"There is no good reason to delay calling a referendum beyond this parliament. To rule one out would do lasting damage to our economy, causing us to fall further behind our European partners," said the letter, signed by 10 mostly former trade ministers including Labour's Mr Peter Mandelson and Conservative's Mr Michael Heseltine.

In the letter, the ex-ministers pointed to a study written by three economists from the Inter-American Development Bank and released by the pro-euro lobby group Britain in Europe.

The study found that Britain's trade would have increased by 7 per cent each year had it joined the European Monetary Union in 1999. The ex-ministers argued that nine of the 12 euro countries were both richer and more productive than Britain.

On June 9th, British Chancellor of the Exchequer, Mr Gordon Brown, is widely expected to say the economic tests for euro entry, which he set back in 1997, have not yet been met. But government sources say Mr Blair wants the assessment to be written in a way that keeps open the option of a referendum before the next election, due by 2006. Ministers are due to discuss Mr Brown's economic assessment on euro entry at a cabinet meeting this Thursday and Mr Blair has said their opinions will be taken into account.

Meanwhile, Swedes opposed to joining the EU's common currency extended their lead over the pro-euro Yes camp by four percentage points to 18 points in a fresh Gallup poll published yesterday. The No side's lead was the biggest in any opinion survey released since Prime Minister Mr Goran Persson's announcement in November that Swedes were to vote for or against joining the euro in a referendum on November 14th.

Gallups telephone poll of 1,010 Swedes gave the opponents 50 per cent against 32 per cent for the supporters.

The previous survey by the same research institute released on May 26th put the anti-euro No camp 14 points ahead of supporters at 49-35 per cent.