'He's hardly the first politician to have the odd fling,' â¿“ Lady Archer, in court for her husband once again

Mary Archer produced the black leather jewellery box with a flourish. Inside, nestling in the black velvet, was a necklace of blue jadeite and heavy silver her husband, Jeffrey, had given her. Then came the punchline – a similar necklace had been presented to another woman.

"It was given as a gift to a woman who did indeed play a large part in Jeffrey's life," she said. "It was given to Margaret Thatcher on the 10th anniversary of her premiership," she added triumphantly, quickly looking around court number 8 to see the effect. She then took out and waved a card in a plastic folder "a thank you note from the Prime Minister".

The moment of theatrics, one of many in a riveting day, was an attempt by Lady Archer to dismiss claims of her husband's serial philandering made during his Old Bailey trial for perjury and forgery.

Angela Peppiatt, his former personal assistant, had said that two sets of the expensive South African jewellery were bought, one for his wife, the other for the principal mistress, Andrina Colquhoun. Lord Archer of Weston-super-Mare had installed the latter at his London flat and the former in the Old Vicarage in Grantchester.

Asked whether she and her husband led separate lives, Lady Archer snapped: "It is complete and utter nonsense." Lord Archer's counsel, Nicholas Purnell QC, asked whether the remarks she made about her marriage being "happy and full" were correct in her famously "fragrant" appearance in the 1987 libel case. She smiled and nodded. "They were indeed, Mr Purnell."

But by the end of a tense, hot and often acrimonious day in court, Lady Archer had to admit that her husband had indeed cheated on her with Ms Colquhoun and she had to endure the humiliation of reading of it in a newspaper after a call from a colleague. She said she confronted her husband and he had promised to end the liaison. Earlier in the trial, the court had been told the affair had continued in secret.

Mary Archer's evidence in the witness box came 13 years, 11 months and three weeks after she last taken the stand on behalf of her husband. Then he had sued the Daily Star and won a record £500,000 in damages after the newspaper claimed he had sex with a prostitute, Monica Coghlan, at a seedy hotel in Victoria. There had been wistful speculation among the attendant media that she would be giving evidence this time as well, after several cameo appearance during the trial. One could almost feel the heady mixture of surprise and anticipation in the press benches and public gallery as she walked into court at 10.56am.

Lady Archer glanced briefly at her husband, sitting in the dock, and he smiled back. He had refused to give evidence himself in his defence. Their sons, William and Richard, sat against the wall, as she made her way to the witness box made of blond wood.

Lady Archer was perfectly groomed in a black suit with purple pipings, earrings of black stone set in gold, not a hair out of place on her permed dark head. A slim, highly attractive and somewhat formid- able figure at 56. The journalists were convinced that what she was wearing was a designer outfit, but no one felt confident enough to approach her and find out what it was.

One of the abiding memories of the 1987 trial was the late Mr Justice Caulfield's famous (or infamous) summing up, which eulogised the "fragrant" Mary Archer. Yesterday there was no such sign of infatuation from Mr Justice Potts. At one point he interrupted a soliloquy in response to a question with: "If you listen to the question then answer, it will be a lot better. That's the way we do it here."

Later, during an exchange with the Crown counsel, David Waters QC, the judge said: "I think it is Mr Waters who is asking the questions here." At another point he interjected: "Please give evidence about matters that you know of. Let me be quite clear – you are giving evidence here, he [Lord Archer] is not."

But as Lady Archer started to give evidence there was no stopping her. Her answers came in a torrent of words delivered in a cut-glass voice that veered increasingly towards exasperation as the questioning got more and more personal.

Lord Archer, 61, sat in the dock, listening and watching his wife intently. He denies three charges of perverting the course of justice, two offences of perjury and one of using a false instrument. His co-defendant, Ted Francis, 67, denies one charge of perverting the course of justice.

The court had heard that during the Eighties Lord Archer had a long affair with Ms Colquhoun. There had also been claims that he was seeing other women. But his wife denied yesterday that her marriage had been under strain. "The only strain was that engendered by the libel trial, not so much a strain on our marriage as a strain on our lives. I think we explored the further reaches of 'for better or for worse' than some other married couples and that was a very traumatic time."

She said she was "disappointed" to discover in 1999 that the Tory peer had asked his friend Mr Francis to lie for him to provide an allegedly false alibi for the 1987 libel trial. Lord Archer had said he wanted Mr Francis to cover for him because he was seeing a "close female friend". Lady Archer said: " It was trivial but I knew it would be catastrophic" to his hopes of becoming Mayor of London.

Mr Waters asked: "Were you aware your husband had an affair with Andrina Colquhoun as she was then?" Lady Archer paused, looked at him and said: "Yes, I was, Mr Waters." She said she first saw an item in the William Hickey column [in the Daily Express] after being warned by a colleague at Cambridge University where she worked "about 18 months before the libel case".

Lady Archer denied she "covered up" the affair to help the political career of her husband who was being considered for the deputy chairmanship of the Conservative Party. She said: "Cover up, Mr Waters? No, well, maybe make light of it. By the time I discovered it, it was essentially in the past. Wives are not necessarily the first to find out about these things. He would hardly be the first aspiring politician to have had the odd fling."

Lady Archer told Roy Amlot QC, for Mr Francis, she had confronted her husband and he had promised to stop. Mr Amlot said: "I am sorry to pry further; when you confronted him, was it in the form of an ultimatum?" Lady Archer said: "I tend not to issue ultimata. Let's say it was a fairly free and frank family discussion."

She was told Ms Colquhoun had admitted the affair continued until 1987. Lady Archer said: "You have heard more than I have heard." The court was read a speech by Lord Archer's barrister in the 1987 trial in which he said "there is not a suggestion that Jeffrey Archer is a man who has affairs".

Mr Waters asked: "Did you have a feeling of injustice that the jury was being misled?" She replied: "I truly have no recollection of a reaction of any part of what I read in this transcript." The judge leant forward. "No recollection?" Lady Archer shook her head. "I truly do not recall. I do recall feeling somewhat tense throughout the trial."

The judge called for a short adjournment after Lady Archer finished her evidence. As she left the court, Lord Archer emerged from the dock and patted her shoulder. "You have done brilliantly, darling," he said. She looked absolutely drained.