Silvio Berlusconi, the Italian Prime Minister, has written to UK counterpart Gordon Brown to demand support for a $10bn (£6.8bn) deal to build Eurofighter combat jets.
Defence sources said that Mr Berlusconi sent the letter on Friday, after the Treasury declined to go ahead with a £1bn payment for 16 jets. The order was part of a four-nation deal, between Germany, Spain, the UK and Italy.
Angela Merkel, the German Chancellor, called Mr Brown to lobby for his support last week. It is understood that she intends to telephone him again in the next few days, while Spanish Prime Minister Jose Zapatero was planning to contact Mr Brown this weekend.
Despite budget cuts, manufacturers from all four countries were hoping to sign a contract soon with the four nations. However, the UK has argued that it does not have room in its defence budget to fund the deal at this time.
The manufacturers are the UK's BAE Systems, Italy's Finnemeccanica and EADS of Spain and Germany.