John McCain yesterday denied allegations of a romantic relationship with a lobbyist and rejected a newspaper report that he granted her clients political favours.

“I’m very disappointed in the article,” the presumptive Republican presidential nominee said at a news conference while his wife, Cindy, stood at his side. “It’s not true.”

The front-page article in The New York Times landed like a bombshell in the presidential campaign and has raised as many questions about the newspaper’s standards as the ethics of Mr McCain. It had planned to publish the article in December — before the Iowa and New Hampshire contests — but did not run it at the time after frantic lobbying by Mr McCain and his lawyers.

The report suggests that eight years ago, during his first run for the presidency, Mr McCain was romantically involved with Vicki Iseman, a telecoms lobbyist then in her early 30s. The newspaper quoted anonymous aides saying that they had urged the Arizona senator to stay away from Ms Iseman — “to protect the candidate from himself” — and that she was herself warned to keep away from the candidate. It offered no evidence of any relationship.

Mr McCain, 71, described Ms Iseman as a friend, whom he sees on various occasions in Washington, “particularly fundraisers and receptions and before the [Senate Commerce] committee”. He said that he last saw her several months ago, when “I bumped into her at some event”. Asked if he was closer to her than other lobbyists, he replied: “No.”

The New York Times says that John Weaver, a former top strategist and now a campaign adviser, told its reporters that he arranged a meeting with Ms Iseman at Union Station, Washington, “after a discussion among campaign leadership”. Bill Keller, the Editor, said that its two anonymous sources were disgruntled former aides.

Mr Weaver said that he arranged the meeting with Ms Iseman in December 1999 because he believed her “comments about having strong ties to John’s committee staff, personal staff and to him I felt were harmful and not true. And so I informed her and asked to to stop and desist.”

Mr McCain was asked about the allegation that he was warned by Mr Weaver to stay away from Ms Iseman: “I never discussed it with John Weaver. As far as I know, there was no necessity for it. I don’t know anything about it.” He said that if there had been concerns among his aides about Ms Iseman, they had never communicated it to him.

Ms Iseman, in the New York Times article, denied that there was any relationship. Her lobbying firm said that it was based on fantasies and without merit.

Mrs McCain said: “My children and I not only trust my husband but know that he would never do anything to not only disappoint our family, but disappoint the people of America. He’s a man of great character.”

Mike Huckabee, the former Arkansas Governor who is Mr McCain’s remaining rival for the Republican nomination, called Mr McCain “a good, decent, honourable man”.

In late 1999 Mr McCain twice wrote letters to the Federal Communications Commission on behalf of Florida-based Paxson Communications — which had paid Ms Iseman as its lobbyist — urging quick consideration of a proposal to buy a television station license in Pittsburgh. At the time Lowell W. “Bud” Paxson, Paxson’s chief executive, was a big contributor to Mr McCain’s 2000 presidential campaign. Mr McCain did not ask the FCC to approve the proposal.

Mr McCain wrote the letters after receiving more that $20,000 in contributions from Paxson executives and lobbyists. Mr Paxson also loaned Mr McCain his company’s jet at least four times during 1999 for campaign travel.

“Riding on the airplane was an accepted practice,” Mr McCain said. He added that he supported a change in rules since then.

Mr McCain denied doing any favours for Ms Iseman or the company. “I’ve served this nation honourably for more than half a century,” he said. “At no time have I ever done anything that would betray the public trust.”

The story appears to be rallying conservatives behind Mr McCain, galvanising the base of the party that has been openly hostile to him. The Republican Right loathes The New York Times, which it views as a bastion of liberalism.

In a written statement Bill Keller, the New York Times executive editor, said: “We think the story speaks for itself.” He added: “On the timing, our policy is we publish stories when they are ready.”

Times Recommends

• Rio Tinto four held as China prepares case
• Diplomats must keep heads down and trousers up
• When in Rome should one make like Berlusconi?