Tony Blair will today give the clearest warning yet that Britain risks being left behind unless it joins the single currency.

Speaking in Birmingham this morning, the prime minister will say that Britain has too often stood back from key developments in Europe's history.

He will tell his audience that Britain's involvement in Europe has been a tragic "history of opportunities missed in the name of illusions".

His intervention comes as reports suggest the chancellor is also preparing to strike a more positive note on the euro. Gordon Brown is said to have reassured cabinet colleagues that he wants Britain to join the single currency.

The Sun predicts the government has now decided to hold a euro poll on the same day as the next general election.