Eight years into her marriage, Janet Coggin discovered that her husband worked for the KGB. EMMA COOK met her
It is easy to assume that the ultimate act of betrayal any spy can commit is against his, or her, own country. A spy's family, though, will tell you a different story. The real deceit will always lie closer to home.

Janet Coggin, now 62, was married to KGB master spy Dieter Gerhardt for eight years before she discovered the true nature of her husband's work - for all that time she believed she was living with a highly ambitious British naval officer. One brief and brutal conversation reduced those years to a fiction; the man she thought she had married didn't even exist.

At that time - the mid-Sixties - they were living in South Africa. She was a full-time mother with three children and Gerhardt was constantly travelling abroad. "He came back on leave and asked me if I wanted to go for a walk. Later he told me it was in case the house was bugged. It's hard to imagine now, I know, but I really didn't have a clue at the time.

"I refused to believe him at first. He fantasised about everything and was always telling stories about places he'd never been to." He would, for instance, regale friends about his love of fishing and then admit to her later that he'd never fished in his life. So when he told her the Russians had ordered him to recruit her and that they wanted a husband- and-wife team, she thought he'd flipped.

"I said it was too fantastic and so he took me back to the house and said, `I'll prove it'. He showed me a letter with a tiny black dot in it and then under a powerful magnifying glass I saw in this pinprick a whole letter."

Softly spoken, Coggin is a picture of Home Counties decency, dressed in crisp white linen shirt and a navy jacket. The world she inhabits seems more Joanna Trollope than Ian Fleming or Alistair MacLean and presumably she thought that too - until her husband proved otherwise. She even looks and sounds a little like Lindsay Duncan - a favourite casting choice for anyone adapting a Trollope for the televison - with those durable good looks: aquiline features and striking blue eyes.

In many ways, his revelations must have been more undermining than a sexual infidelity. One affair seems a minor concealment compared to an entire identity, a whole way of life. To this day she still wonders if he married her for convenience or love. And which identity was really him? The ruthless spy trained to kill on sight, who routinely lied to colleagues and loved ones, or the initially affectionate husband who was keen on family outings and holidays? "I'll never know now. All I do know is that he seemed so normal in the early days and then he seemed much tenser."

It is at this point that you do begin to wonder how it is possible to live with someone for so many years and not intuit, at some level, that all is not as it should be. In her account of the marriage, written rather archly in the third person, there are certain anecdotes that make Gerhardt sound like a farcical combination of James Bond and John Cleese. Like the time Coggin opened the door of the airing cupboard to see her husband crouched in the bottom, screaming, "Get out, get out". (Later she found out he was developing microfilm.) In another episode he seemed extremely upset when a box of his matches disappeared. When she bought others he screamed, "I have to have the other box". (He had written a code on the back). Then there was the question of money; Gerhardt always had endless amounts of it, far more than the other naval families.

Just as peculiar is how little she challenged these irregularities. Of the money, she said it wasn't unusual to receive generous overseas pensions. And she had already justified his erratic behaviour. "I thought he was mentally ill. I was relieved in some ways when he told me he was a spy. At least I knew he wasn't mad. I was very worried the children could inherit it."

Coggin met Gerhardt at a wedding when she was 21; he was at naval college in Plymouth and she was working in a refugee camp in Peterborough. Four months later they married. "He was terrific fun and terribly attractive. He was very popular with everybody and could be whatever people wanted him to be."

Her account paints a rather more austere picture, one where Gerhardt seems more brutal, remote and heartless than charming and urbane. In fact, the two of them seem utterly polarised; she a liberal, he a traditional apartheid-accepting South African, she passive and unquestioning and he unreasonable and domineering. They were, she admits, "like chalk and cheese".

She describes in the book how, when she was pregnant with her third child, he banged his fist on the table and ordered her to have an abortion. (She refused.) Yet in the next sentence she feels sorry for him because she "sensed he was in some difficulty". When he tells her matter-of-factly that if she won't be a spy he will have to find another wife to put "on the Russian's payroll", she admits to a "sense of outrage" but is divided about leaving him. "Hadn't she promised for better, for worse?" she writes. "And really meant it?" At another point, he tells her that he could have her "wiped out" and her death disguised as a suicide.

Neither in her book nor in person does she ever express outrage. "There is no resentment. What's the point of being angry?" she asks softly, then she smiles apologetically, looks down and clasps her hands in her lap meekly. "What was so consuming when I first found out was how to make a normal life for my children. In contrast, blame and anger seemed so minor. There wasn't room for asking questions." Not even why he chose to be a spy? "Yes, I have asked that. I don't think it was ideology - I certainly never saw any evidence of that. I think it was a mixture of a lot of things. He liked the way of life, the power and money and the feeling that he was fooling people."

Even that doesn't seem to upset her unduly, "because everyone does their own thing," she says. "I'm only responsible for myself and somehow I blundered into his responsibilities."

Her attitude to his behaviour probably says as much about the time in which she married - and the milieu she married into - as the bizarre circumstances she was forced to confront. To some extent her acceptance of the mood swings, the unexplained trips away from home and the continual subterfuge was precisely what was expected of a Forces housewife in the early Sixties. "It was very unpleasant," she says with that same mildness of tone, as if recalling a badly cooked meal. "You simply try and put it to one side, don't you?"

As soon as he told her the truth - and asked her if she, too, would like to become a spy - she left him. She went to Ireland with the children to start a new life and divorced him a year or two later. She built an independent life, working for Amnesty International and teaching children with learning difficulties, and met her current partner.

Still, though, she couldn't shake Gerhardt from her life. He would write long letters instructing her how to discipline the children. Even worse, the children would have to stay occasionally with Gerhardt and his new "spy-partner wife" - Coggin believed her life was under threat if she refused. During one of these visits, her eldest child overheard Gerhardt and his "wife" talking about whether to get rid of her or not. "I had to pretend to them that it was just Daddy being funny and that everybody has a different sense of humour," she says.

For years she couldn't tell anyone the truth of her situation, not even her father. She was terrified. "I spent most of my years of motherhood grateful for not being murdered," she says. Even now she rarely discusses those years with her children, now grown-up. She always felt she had to cover for Gerhardt's lack of affection towards them. "I always used to give them birthday and Christmas presents and say they were from Daddy."

Gerhardt was finally arrested in 1983 by the FBI for selling Nato secrets to the Soviet Union and sentenced to life imprisonment. Released four years ago, he now lives in Switzerland.

Last year Coggin decided it was time to break her silence. "After so long I wanted to talk about it. It was hard not to be able to confide in anyone for so long. Now I just think everyone is given their own set of difficulties and this happened to be mine. I dealt with it all long ago.

"It may sound strange to you but it really does feel like a different part of my life. I simply put it to one side," she says crisply.

Ideals aside, Coggin may have made rather a good spy after all.

`The Spy's Wife' by Janet Coggin is published by Constable, price pounds 16.99.