But the absurdity is that while one part of the Home Office has patiently collaborated across Whitehall on preventative strategies to stop human trafficking, and how to protect the intensely vulnerable individuals caught up in the trade, another part of the Home Office has put forward a package of measures on migration which include a proposal to do the exact reverse. It's the kind of one step forward, one step backward form of policy making which leaves campaigners in despair.

The place to understand the issue properly is at the support organisation for domestic migrant workers, Kalayaan. Its offices are in a little alley tucked behind the beautiful stucco houses of Holland Park that gleam with wealth. As London's plutocracy booms, fuelled by the influx of an international elite, the stories of the women I met there represent the seamy underside of London's new position as global metropolis.

Take Maggie. A young west African woman, she came to the UK three years ago with her employers. She looked after their children every day until late in the evening but was never paid - her employers claimed she had to pay back her air fare. In addition, her employers made her go out to work as a cleaner every day - and took her wages. Maggie opens her diary where she has kept an account of the thousands of pounds she has had to give them. What trapped her in this forced labour was that her employers refused to hand over her passport unless she paid £4,000. A few months ago she ran away.

Or take Rina. An Indian woman with a broad smile and a tragic story of abuse in two families. Long hours, little food to eat and even, she admits, rape in her last job. But with her extended family in India dependent on her remittances, she can't return home. She now cares for an elderly woman with dementia seven nights a week. She has nowhere to live and spends the days on the street or in the local church.

These are the kinds of women that the government's proposal will affect. It's a few thousand perhaps - but the proposal is likely to lead to gut-wrenching suffering because it affects one of the most vulnerable forms of employment - domestic migrant work. Hidden in the privacy of the home, cut off from any kind of wider social contact, these women have working lives that are impossible to regulate. They often work punishingly long hours for low pay and little food: 60- or 70-hour weeks are common. With little knowledge of the UK, they are dependent on their employers to ensure that their visa and tax status is legal and it's a dependence some employers ruthlessly use to exploit them.

All of this the government seemed to have recognised back in 1998 when, after years of campaigning and with a lot of backbench support, the new Labour government pushed through a small but crucially important measure for these domestic migrant workers: they were given that most basic of employment rights - the right to change their employer. They no longer had the bleak choice of remaining with abusive and exploitative employers, or facing illegality and deportation. Providing they were still in full-time domestic work, they could renew their 12-month visas and stay in the UK. As Maggie's and Rina's cases illustrate, this protection still doesn't prevent abusive employment, but at least it provides a legal option to leave it.

Wind the tape on nine years and even this minimum protection is to be withdrawn this autumn. The thinking is that such unskilled labour is no longer required from outside the EU and that the new accession countries can provide cheap domestic labour. But the government is not going to stop all non-EU domestic migrant work - that might compromise the attractiveness of the UK to those rich, often highly skilled employers who bring them in (the same consideration weighed on Tory policy in the 90s). So the nonsensical compromise proposal in the government's Making Migration Work for Britain policy is that domestic migrant workers can come to the UK with their employers but they can't change jobs - and they can only stay for six months. The thinking is that that's enough time to train up an eastern European before sending the Indonesian or Sri Lankan nanny home.

The policy may make sense in the corridors of the Home Office, but it ignores the fact that there is a growing demand for carers in the UK, for both children and older people, and young eastern Europeans don't fill all the vacancies, particularly for the difficult work of caring for those with dementia. Meanwhile the supply of migrant workers in the developing world desperate for such work is enormous. With both a strong demand and an equally buoyant supply, the fear is that the policy will simply force employment underground into all the problems of exploitation that dogged it through the 80s and 90s. Such is the difficulty of recruiting flexible decent childcare or elder care, employers will be prepared to dodge the immigration rules and migrant domestic workers will find themselves trapped in illegal employment.

The desperate stories of Maggie and Rina are evident in millions of households across the world; one of the most valuable exports of many developing countries is the caring labour of women. Remittances from nationals working abroad are worth more to some countries than aid. But this trade of care is almost always accompanied by virtually zero employment protection - old stereotypes about this being women's work and not real labour still linger. In 1998, Britain was regarded as a pioneer for the modest measure it introduced. Canada is one of several countries which has attempted to provide some protection since. Nine years on, Barbara Roche, who implemented the measure as a Home Office minister after campaigning for such women as an MP in opposition, wonders how the history could be forgotten and the progress reversed.

At a point when we are trying to reckon with the history of 200 years ago, it would make a nonsense of our professed good intentions if we can't stretch our memory back less than a decade. Perhaps it's so easy to forget the plight of these women because the Maggies and Rinas are invisible - indistinguishable on the street or supermarket, and most of the time, discreetly working behind front doors. Just remember that the polish on London's mansions' brass knobs and the scrupulously scrubbed front steps were done by someone.

m.bunting@theguardian.com