She is asked by John Walsh in an interview if she has any advice for Cherie Booth, wife of the Labour leader, Tony Blair. She replies: "Oh, I wouldn't presume. I think we all have to make of this job what we can. But I've no brief. She'll do it her way."
Mr Walsh says in the interview, in the Independent magazine, that he has double-checked his tape recording and there is no doubt that Mrs Major says "She'll" and not "She'd".
The apparently small difference is crucially important. Mrs Major is clearly talking about the role of prime minister's wife, using the future tense about "this job", in an interview at Chequers, the Prime Minister's country residence.
If it is a slip, it is a revealing one, suggesting that she shares the views of the rest of the country. Labour has an average lead in opinion polls of 22 percentage points and two-thirds of the voters expect Mr Blair to form the next government.
Mrs Major's admission will be particularly embarrassing for her husband because Conservative strategists earlier this month announced that she would have a higher profile in the run-up to the election.
Officials at Conservative Central Office briefed selected journalists on Tory newspapers that Mrs Major was regarded as "an asset", and contrasted her with Ms Booth, a successful barrister and QC, whose image was said to be less voter-friendly.
But Norma and John Major are believed to have been irritated with Brian Mawhinney, the Tory party chairman, about the way newspapers were encouraged to report the fact that she would be at the Prime Minister's side during his pre-election tours.
In today's interview, she dismisses as "tacky" the fashion for American political wives to play a front-line campaign role. Both Elizabeth Dole and Hillary Clinton paid fulsome tribute to their husbands, Bob and Bill, at their respective Republican and Democrat party conventions in the United States last month. Asked if she could see herself doing that, she replies: "No, I couldn't do that! I wouldn't do that, no matter what the pressure, I think it's so tacky."
Last weekend Mrs Major gave a rare television interview, seen as part of the plan to project her during the pre-election campaign, in which she nevertheless rejected the description of her in some of the tabloids as the "Tories' secret weapon".
Ms Booth, meanwhile, is guest editor of the mass-market monthly magazine Prima in which she reveals a few carefully chosen secrets of the Blair household, such as the fact that she is a "keen knitter" and that her husband "knows where the washing-machine is".
The Labour leader's wife has herself been criticised by the Tory press for some of her political statements. In February, she was attacked for telling a Society of Labour Lawyers reception that Lord Irvine of Lairg, Labour's legal affairs spokesman in the House of Lords, would definitely be in her husband's Cabinet.
Mrs Major has played an uncertain supporting role to the Prime Minister, ever since he was succeeded Margaret Thatcher in 1990. It was widely speculated that she was unhappy with the pressures that would be put on her family, and she refused to move into Downing Street, preferring to stay at their Huntingdon home.
In her interview she initially says "we'll cross that bridge when we come to it", when asked if she would miss 10 Downing Street. "We're not planning for it just yet."
But then she appears to allow her assumptions about her husband's political future to show through, just as her body language on the steps of Downing Street seemed to give away her reluctance to be there six years ago.
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