Sir Edward Heath today launches a devastating attack on the "fanatical opponents" of Europe and the single currency within the Tory party, in what will be a bitter blow to its vehemently Eurosceptic leader Iain Duncan Smith.
Friends of the former prime minister have made it clear that his reference, in an article for today's Independent on Sunday, to the anti-Europeans who had "staged a coup in the Conservative Party and again were rejected by the electorate" is a clear criticism of Mr Duncan Smith and his anti-euro Shadow Cabinet.
It comes after several weeks in which the beleaguered Tory leader has been repeatedly undermined by senior figures within his own party, raising renewed questions over his future.
Sir Edward, the prime minister responsible for taking Britain into Europe 30 years ago, writes that the sort of "fanatics" who opposed him were now "focusing their attention on the euro".
In the article – backed by the pro-single currency group Britain in Europe – Sir Edward also delivers a challenge to the current Prime Minister, who is yet to launch a convincing campaign for euro membership, writing: "I look forward to campaigning vigorously for a 'Yes' vote."
Sir Edward's comments came as Bill Morris, general secretary of the Transport and General Workers' Union and a close political ally of the Chancellor, Gordon Brown, urged the Government to rule out euro membership ahead of the next election. Mr Morris warned: "You can't have the euro and the continued reform of public services."
While Mr Morris insisted he had not discussed his views with the Chancellor, the Treasury clings to its five economic tests, due to be assessed next summer, as the basis for any decision on a proposed referendum. Mr Brown and his aides are thought to be less enthusiastic about membership than Tony Blair.
But although No 10 is understood to have told the Britain in Europe campaign to "move up a gear" in the new year – assisted by its recent move to new, bigger premises – Mr Blair has so far fought shy of firing the starting pistol for a referendum campaign.
However, Sir Edward's article makes clear the case for entry. He writes: "It is my view that if we are serious about our future in Europe, and particularly the single market, then we will have to join the euro.
"Many of the benefits of the past 30 years will be at risk if we do not. We cannot be half in the single market and half out. We cannot be half in Europe and half out ... A 'No' vote will permanently relegate us to the second division of European nations."
Sir Edward's views will add to Mr Duncan Smith's woes as he prepares to return to the House of Commons early in the new year on the back of prolonged personal criticism and poor poll results.
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