Cameron plans to drop visa that saved his children's nanny

David and Samantha Cameron recruited their nanny from a charity that helps immigrants to escape abusive bosses, The Independent on Sunday has learnt.

The news comes as the Government considers abolishing a visa which until now has enabled people such as Gita Lima to change employers to escape exploitative work. Under proposed new rules it would not be possible for women like her to work for anyone other than the employer who brought her into the country.

Ms Lima, originally from Nepal, has been working for the Cameron family for years. She was recruited after the Camerons advertised the position with the charity Kalayaan, which specialises in helping migrant domestic workers fleeing exploitation or abusive employers.

Ms Lima helped to care for the couple's severely disabled son Ivan, who died in 2009. She is understood to have been going through the process of getting permanent immigration status last year.

On Tuesday, the Government will mark Anti-Slavery Day by trumpeting its desire to combat people-trafficking, with David Cameron hosting a tea at No 10 to honour the occasion on Wednesday. But critics say the Government's proposed immigration policies would leave foreign domestic workers more vulnerable.

Jenny Moss, a community worker at Kalayaan, said: "Mr Cameron clearly understands the issues faced by migrant domestic workers and the reason why the right to change employer is so important to protect them from violence and exploitation. It seems as though he either does not know about the policies proposed in the Home Office, or he has not made the connection between his government's proposals and the horrific consequences they could have for people like his own nanny."

A UK Border Agency consultation which closed last month proposed ending the visa for overseas domestic workers or keeping it but removing the right to change employer or seek settlement in the UK. The overseas domestic workers visa was introduced in 1998 with the specific purpose of protecting this vulnerable group, who are easy prey for abuse and enslavement as they are usually brought in alone by their employers.

The proposal is part of the Government's pledge to cut net migration to tens of thousands by 2015. According to the proposal, if the visas are kept, it would be under the proviso that they could not be transferred to a new employer or end in long-term settlement in the UK, making it much harder to escape abusive bosses. If enacted, it would mean employers such as the Camerons would not be able to give people a second chance at a working life in the UK.

Research by Kalayaan suggests specific visa protections curbed the abuse suffered by domestic workers. A survey two years before the visas came in found that 89 per cent were working seven days a week; 100 per cent were working an average of 17 hours a day; 87 per cent were psychologically abused; and 39 per cent physically assaulted. In 2010, when the visa had been in place for 12 years, the number subjected to serious abuse had declined, with 54 per cent suffering psychological abuse, and 18 per cent experiencing physical abuse.

A Downing Street spokesman said the issue was "a private matter", adding: "We need an immigration system that is fairer and more honest. At the same time, the Government remains committed to tackling illegal immigration and human trafficking."

Audrey Guichon, an expert on domestic workers at Anti-Slavery International, said: "The Government knows that prior to the introduction of the domestic worker visa there were appalling levels of abuse experienced by migrant domestic workers in the UK. Reductions in abuse were specifically due to the introduction of the visa and the protection it offered, especially the right to change employers."