Citing three examples from the last few days, the sources said that Nissan "chiefs" do not fear life under "chameleon Blair"; "Big Brother Blair" is not using the party's campaign computer to log every public statement made by Labour rebels; and Tony Blair has no plans to promote "fat cat" millionaire backbencher Geoffrey Robinson to his Cabinet.
The sources said all three reports were untrue, and the party later issued an effusive letter from Ian Gibson, managing director and chief executive of Nissan (UK), repudiating Monday's Daily Mail report that 1,000 new Nissan jobs were at risk following "a secret meeting this summer between bosses of the Japanese car giant and the Labour leader".
The Mail quoted a Nissan source as saying: "Tony Blair talked to us about his strategy. But he is a chameleon. He changes his colours to reflect whatever is around him."
The report could have been tailor-made to fit in with the Tories' "New Labour, New Danger" campaign. With no substantiation, but remarkable precision, it said Nissan had calculated that a Labour government would reduce car sales by 5 per cent, or 100,000 vehicles.
It also said: "Labour's support for the Social Chapter - which would force up costs and make British workers less competitive than their foreign rivals - is another factor in their decision."
But Mr Gibson said in a letter to Mr Blair yesterday - copied for publication - that no such meeting had taken place; Nissan was the only car manufacturer in the country to belong to Labour's Industry Forum; and the company shared Labour's views on the need for extensive employee-training, a stable macro- economy and low inflation as the foundation for growth.
As for a threat to impending investment, Mr Gibson said: "There is no decision on future investment or current production at Sunderland that would be affected by the composition of the next government.
"You have my assurance that Nissan has no negative view of a potential Labour government and that our plans will continue to be made as so far - in the best interests of our customers and employees."
It is expected that Nissan's main European board, meeting in Amsterdam today, will endorse Mr Gibson's repudiation of the highly damaging Daily Mail story.
The report on Mr Blair's alleged plan to give Mr Robinson a front-line role, with some Labour "insiders" predicting that he could become President of the Board of Trade, was even more scornfully dismissed by a Labour leadership source yesterday.
Mr Robinson - MP for Coventry North-West, former chairman of Jaguar, moving force behind the international engineers TransTec, new owner of the New Statesman magazine, and owner of the Italian holiday villa used by Mr Blair this summer - could well become a middle-rank minister, but a Cabinet post would be a remarkable leap for a man not known for his political touch.
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