Supporters of withdrawal from the European Union suffered a major set-back as a senior American official warned that the move would make it more expensive for British firms to export to the United States.
Michael Froman ruled out negotiating a new trade deal with the UK in the event of a vote to leave the EU in the referendum promised by David Cameron by 2017.
His warning came as the Prime Minister held fresh talks over renegotiating the terms of Britain’s EU membership with other European leaders.
Campaigners for “Brexit” argue that the UK would be able to strike its own trade agreement with the US – the biggest market for British goods after the EU – if it left the 28-nation bloc.
But Mr Froman, the US trade representative, insisted that was not the case, telling Reuters: “We’re not particularly in the market for [trade agreements] with individual countries.”
He said: “I think it’s absolutely clear that Britain has a greater voice at the trade table being part of the EU, being part of a larger economic entity.”
Sir Nigel Sheinwald, former British Ambassador to the US and EU, said: “Michael Froman’s comments present those wanting to leave the EU with an inconvenient truth – that a major trade and investment partner, the US, sees no influential role for the UK in international trade negotiations if we go it alone.
“Inside the EU will we have the clout to promote the open trade access our country needs. Outside the EU we would stand in line behind the big trading blocs.”
But Rob Oxley, spokesman for the Vote Leave campaign, said: “Britain currently has no trade deal with the US, as the EU has failed to get one over the last 40 years. This means if we leave the EU there would be no change to our trade with America, but we would take back control over trade policy and would be able talk to Washington directly, instead of hoping the EU will do it for us.”
Questions over the impact of “Brexit” were also raised yesterday by the Standard and Poor’s credit rating agency, which warned that Britain would lose its top AAA rating if it voted to leave the EU.
Some EU leaders have said they have not yet seen detailed proposals from Britain over a reformed relationship with Brussels, raising doubts on whether significant progress can be made at the next leaders’ summit, which takes places in December.
But Mr Cameron, speaking at the Northern Future Forum summit in the Icelandic capital Reykjavik, said the pace would be stepped up in coming weeks. During the summit he met the leaders of the EU members Sweden, Finland, Estonia, Latvia and Lithuania.
The Prime Minister has promised to provide details of his proposals in a letter to European Council president Donald Tusk early next month.
He said: “I would argue it’s going well. I said I’ve launched the process and it's got under way. That was accepted at the June European Council. There was an update in October. Now the pace will quicken.”
The former chancellor Kenneth Clarke said he would be horrified if any of the Prime Minister’s potential successors campaigned for Britain to leave the EU.
Mr Clarke, who ran against Mr Cameron for the leadership, warned contenders that it would be “totally irresponsible” to urge withdrawal to gain a tactical advantage over their rivals.
He said another Tory civil war on the issue, similar to that which hit the party in the 1990s, would lead to the Conservatives losing power.
“If we start going back to Euro-wars again then all the work that David Cameron has done to get us back into office will be completely thwarted because we’ll get thrown out again,” he told the House magazine.
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