A senior News International journalist warned Labour that the company's papers intended to "turn on Ed Miliband and his staff" days before allegations were published in The Sunday Times and The Sun about his strategy director Tom Baldwin.
The Independent understands the warning was made to a Labour spokesman hours after Mr Miliband had called on Wednesday for the resignation of News International's chief executive Rebekah Brooks.
Three days later, The Sun carried a story claiming that Mr Baldwin had been a heavy user of cocaine. Yesterday, The Sunday Times carried a story which said he had been accused – in a previous job – of hiring a private investigator to "blag" the bank details of the Conservative donor Michael Ashcroft. Mr Baldwin denies the claims.
The broad theme of both allegations had been made in a book by Lord Ashcroft, which was published five years ago. He repeated the allegation surrounding Mr Baldwin's use of private investigators on Friday last week on the website Conservative Home, which he owns.
But the decision by The Sun and The Sunday Times to attack Mr Baldwin has caused tensions at The Times, where he was formerly chief reporter until he accepted the job with Mr Miliband in December last year. In his previous role, Mr Baldwin would not have been able to sanction such payments – suggesting that if the allegations were correct, someone higher up at The Times during the period in question would have had to sanction it.
The last thing Rupert Murdoch would want is a sister paper of The Times precipitating a fresh investigation into the Ashcroft affair.
Mr Miliband denied that his strategy director had been involved in wrongdoing. The Labour leader told the BBC One's Andrew Marr Show: "People are trying to make a comparison between Andy Coulson, who resigned from the News of the World over phone hacking of the Royal Family, and Tom Baldwin, who works for me. I think this is ridiculous, let me just explain why. Tom Baldwin was engaged in The Times newspaper investigation of Michael Ashcroft, about whom there was massive public interest."
Asked about the specific allegations, he said: "Tom Baldwin absolutely denies this. And I have to say that this is pretty desperate stuff, because the Prime Minister must answer the real questions at the heart of this affair – about his error of judgment in hiring Andy Coulson and the mounting evidence there now is about the warnings that were given to him before he brought Andy Coulson into the heart of the Government machine."
Mr Miliband also denied he had "declared war on Rupert Murdoch" but called on him to abandon his bid for BSkyB. "When the public have seen the disgusting revelations that we have seen this week, the idea that this organisation... should be allowed to take over BSkyB... without the criminal investigation having been completed and on the basis of assurances from that self-same organisation – frankly that just won't wash with the public."