Among many poignant moments in our conversation, there is one when the sadness beneath the surface of Catherine Meyer's life brims in her eyes and she falls unusually silent, pushing back intrusive pain. We are talking about the plight of children torn suddenly by one parent from another, when love once shared contorts into revenge. Lady Meyer, the wife of Sir Christopher Meyer, the former British ambassador to Washington, understands the anguish of such separation. For 10 years she struggled to win access to her two young sons, who were virtually lost to her after she and her German first husband divorced.

One consequence of that battle was the formation of her campaign group, Parents and Abducted Children Together (Pact), which strives to stop minors being snatched across international borders and assists police in their search for the thousands of children who go missing every year. Meyer's own situation was a perfect example of the legal minefield that often bedevils such cases and so, to raise awareness of that difficulty, she became a public figure in the United States during her husband's five-and-a-half-year posting.

Yet now, in the quiet elegance of their home in Knightsbridge, London, she is reluctant to be quite so forthcoming about her sons, and for the best of reasons. ?Ten long years passed during which I was only allowed to see them for a total of 24 hours, " she says, ?but today the circumstances have changed. They are adults and they can see whoever they want." The elder, Alexander, a university student in Germany, was the first to express a wish to rebuild their relationship. Then came a similar request from Constantin, currently doing his military service.

?They now call me all the time and visit us regularly here in London, " she says. ?I think Alexander would like to study for his masters in Britain, but for all of us it's still a sensitive experience, this getting to know one another again. And, well, young men don't like their mothers talking too much about them. It's not cool. So I want to be very careful not to do anything that will embarrass them."

Meyer can't hold back completely from going over the cruel ground of her ordeal, however, if only for the sake of others whose e-mails to her reveal comparable stories of suffering, a torment often made worse by the ignorance surrounding the problem. Now, after those few moments when she seemed lost to tears, she says, ?I have met lots of parents undergoing the same trauma, and in their stories there are nearly always three common factors.

?Firstly, when you have had children in your arms since they were babies the wrench of losing them actually feels physically violent. Secondly, there is the terrible anxiety: you never stop worrying if they are all right. Are they being told you didn't want them any more? Are they calling for mummy and crying themselves to sleep? And thirdly, there is this burning sense of injustice."

Meyer detects some of these terrors in the story of 12-year-old Misbah Rana, who until August was known as Molly Campbell and who is being fought over by her divorced parents. Her Scottish mother, Louise Campbell, claimed the child was abducted from their home in Stornoway on Lewis, but Misbah - now with her Pakistani father, Sajad Ahmed Rana, and elder siblings in Lahore - insists she travelled there at her own request, wishing to live more fully in the Muslim faith and no longer wanting to stay with her mother. Last year Louise Campbell was awarded UK custody of her daughter, but the Pakistani authorities recently gave Misbah's father temporary custody until a court hearing in Lahore this month when both parents are expected to put their case.

?I only know of this case from what I've read in the papers but that, to me, is exactly what shouldn't have happened, " says Meyer. ?These stories are always far more complex than headlines suggest, and they should not be played out in public. Once lawyers are involved everything becomes even more acrimonious. In my opinion it is quite criminal to ask children to decide between a mother or a father."

What, though, is the alternative in cases where the hatred between partners is vented in court for common consumption? In matters of child custody Meyer wants to see lawyers replaced by family mediators who make it clear to the warring couple they can fight about finances in court, but not about their children's welfare. ?That should be decided through mediation and then, in private, in the presence of a judge who makes it clear the parents cannot leave his chambers until they have agreed a settlement which becomes legally binding, " she says.

When Meyer's first marriage to Hans Peter Volkmann ended she returned to London with Alexander and Constantin, then aged nine and six. The daughter of a French father and a Russian mother, she holds British and French citizenship, and at the time of her first marriage worked in the City as a commodities broker under her maiden name, Catherine Laylle. In Britain she had been awarded custody of the children and, as their legal guardian, trusted that when they travelled to Germany for a holiday with their father they would be returned. ?But they weren't."

Despite the Hague Convention - the international agreement governing such cases - clearly stating custody issues should be settled in a child's habitual country of residence, the German courts ruled Meyer's sons should remain in Germany and she was banned from seeing them. This also ran against a judgment by the High Court in London that the children had been illegally retained by Dr Volkmann. Over the years, he responded to his ex-wife's attempts to get that judgment rescinded with a legal campaign of procrastination. And that was how things remained until the boys came of age.

The inspiration for Pact came in the US, where Meyer became involved with the US National Centre for Missing and Exploited Children. ?When I came back to Britain I realised just how far behind we were in handling this problem, " she says. Thanks to the Meyers' diplomatic network, Pact has no shortage of influential contacts: its patrons are Laura Bush and Cherie Blair. It also works closely with the Missing Kids website, another American idea, which in the UK operates in partnership with the police, various charities and the private sector.

Catherine met Christopher Meyer in 1997 in Germany, where he was then ambassador. That was when, sick with worry and having lost all her money on so many failed appeals, she turned to the British embassy for help. That our man in Bonn was immediately smitten is evident from his memoir, DC Confidential. ?The door opened and in came a very pretty, fragile-looking woman, " he writes. ?With the greatest difficulty I stopped myself looking at her legs. The plain truth was that I was enormously attracted to Catherine."

As Sir Christopher studied her case, another plain truth emerged: in trying to fight for her children, Catherine had been badly served by the then Lord Chancellor's Department (now the Department for Constitutional Affairs). In fact, last year the parliamentary ombudsman's report into that department's handling of her situation illustrated just how drastically it had failed her by giving incorrect legal advice.

By the time Sir Christopher's appointment in Washington was confirmed, his own marriage had disintegrated and he and Catherine were a discreet item. But, as Washington is a deeply conservative city, he didn't want to begin the most important job in his diplomatic career without regularising their relationship. ?So I was divorced on Monday, " he reflects, ?a free man on Tuesday and Wednesday, got married at Chelsea registry office on Thursday and left for the US with Catherine, now my wife, on Friday." The date was October 31, 1997. ?Hallowe'en, " he adds. ?Most appropriate."

Catherine Meyer's Kafka-esque nightmare with German lawyers was by then at its most intense. The programme of visits between her and the children, which was part of the divorce settlement, was repeatedly ignored. As a result she was obliged to begin the tortuous application procedures over and over again, at great emotional and financial expense.

Meanwhile, the new ambassador was determined the Meyers, like the Clintons, would work as a team. Initially the couple had no intention of publicising Catherine's dilemma, but within three months the Washington Post had got wind of the situation and the story made headlines from then until the end of the Meyers' embassy tenure. American reaction, however, couldn't have been in sharper contrast to the obdurate German legal system and the incompetence of British bureaucracy.

Meyer recalls the Americans' first question was, ?How can we help?", while in his memoir her husband notes that from the presidents Clinton and Bush downwards, the moral and practical support his wife received was enormous, including invitations to her to address committees of both the Senate and the House of Representatives.

The faster her hopes rose because of this positive interest, though, the quicker they were dashed. ?On one occasion we were told we could see the children in Switzerland, and so we went there at the appointed time. And, of course, they didn't show up, " she says. The reason given by the lawyers was that the boys didn't want to meet their mother. ?I know of parents who committed suicide because they could no longer take this kind of legal abuse."

When Meyer was allowed to see her children, it was often under supervision and she would be instructed to speak in German. ?The whole thing was horrendous, " she recalls, ?including the days leading up to the visit and those immediately after. And it must have been the same for them. So you always struggle to know what is best. Do you let go in order not to put them under this pressure? But if you do, they will believe their mother has completely abandoned them, and you cannot let that happen."

Pact's first report, published last year, revealed there has been a steady increase in child abductions and parental child abductions since the mid-1990s. ?The failure to know the precise scale of the problem means that it is not being tackled adequately, " the report said. In the related matter of missing children a similar lack of comprehensive data has hindered the development of a national policy for the UK, but what findings there are indicate that each year at least 100,000 children ?disappear" in Britain, 9000 of them in Scotland. The Pact report said, ?On that basis a child goes missing every five minutes."

Meyer wants the Foreign Office to be far more proactive in pursuing the rights of British parents whose children have been taken abroad illegally. On the domestic front, Pact's key recommendation is for the establishment of a new Home Office division, or alternative body, to drive policy, collate information on the basis of clear and nationally agreed definitions, and set guidelines to ensure the police and other agencies work effectively together.

Pact also wants the creation of a centrally co-ordinated national programme of research dedicated to missing children. In the meantime its own research, with significant funding from the Bridge House Trust, will continue to highlight the ways in which current policy is ?wholly unsatisfactory and requires urgent remedy". But this commitment also means Meyer, the indefatigable campaigner, can never entirely escape the memory of her own ordeal.

Does she talk to her sons about it? She shakes her head. ?Some time they might want to learn about the struggles, but today we are rekindling a very close relationship and I don't want anything to harm that, " she says. ?And to other parents who haven't had this joy of reunion I would say, 'Never give up hope.' It may take years, but children will always be curious to find the mother or father who, they were told, no longer loved them."

Life could not be better now for Catherine Meyer, but the lie that she had discarded her children is the pain that will always mark her. ?It changed me completely, " she says. ?It made me a worrier, a nervous, anxious person with, yes, a hidden streak of pessimism. But for many people there is so much worse suffering in the world."

Visit www. pact-online. org and uk. missingkids. com.