May: Immigration reforms make it harder to catch traffickers and …

The Conservative former prime minister suggested victims would be less likely to come forward to give evidence against traffickers if they believe they were at greater risk of deportation. Mrs May appealed for modern slavery victims to be excluded from measures within the Illegal Migration Bill and for talks with the Government to resolve her concerns. Temporary protection against removal from the UK is currently given to suspected victims of modern slavery or human trafficking while their case is considered.

However, the Bill seeks to remove this protection for people who are judged to have entered the UK illegally, with an exception for those co-operating with a criminal investigation. Mrs May said she has "not seen evidence" to support claims from ministers that the Modern Slavery Act is being abused by people seeking to stay UK, including those crossing the Channel on small boats. The legislation aims to stop people claiming asylum in the UK if they arrive through unauthorised means, including by crossing the English Channel in small boats.

It could result in asylum seekers being detained without bail or judicial review for 28 days before being removed to their home country or a "safe third country" such as Rwanda. The Bill has been denounced by the UN's refugee agency as an effective "asylum ban". Mrs May, speaking during day two of the Bill's committee stage, said: "My fear with this Illegal Migration Bill is that it will drive a coach and horses through the Modern Slavery Act, denying support to those who have been exploited and enslaved, and in doing so making it much harder to catch and stop the traffickers and slave drivers."

Explaining what she thinks the "heart of the problem" is, Mrs May gave the example of a woman from Romania who is "persuaded there's a great job here for her in the UK, is brought here on false papers, put to work as a prostitute in a brothel". She added: "Let's say she manages to escape and meet some people willing to help, she's taken to the police, but the Government says 'you came here illegally, we are deporting you to Rwanda'. The traffickers fear she's looking to escape, (they) take her to one side and explain it's no good doing that because all they'll do is send you to Rwanda.

"We would have handed the traffickers a gift, another tool in their armoury of exploitation and slavery. "Now, the Government might say that it'll be okay if the woman actually helps with an investigation because there is that caveat in the Bill, but that seriously misunderstands slavery and the impact of the trauma of slavery on the victims."

Labour MP Dawn Butler (centre) joins demonstrators protesting against the Illegal Migration Bill in Parliament Square (Kirsty O'Connor/PA)

The MP for Maidenhead said she fears a "lack of proper consideration of slavery" and the experience of the survivors from the Government in connection with the Bill. The former home secretary went on: "There is a move that would be of more benefit in enabling us to catch the slave drivers and support victims and survivors, which would be to ensure those in slavery here in the UK were excluded from this Bill.

"That would mean recognising the intention of the Modern Slavery Act - that those who have been here in slavery in the UK should be protected by the Act regardless of their immigration status. "Now, there may be some of my colleagues who might say, 'Well, doesn't that mean an awful lot of people are going to want to stay here?' and worry about the numbers, but many people brought here into slavery actually want to go home, they don't just want to stay here. "Under this Bill, I fear it is more likely that they will stay here in the UK and be staying here in slavery."

In her concluding remarks, Mrs May said: "I do want to sit down with the Government to find a way through that does not deeply damage the Modern Slavery Act, abandon victims and make it harder to catch traffickers and slave drivers. "I fear this Bill is going to do all of those things." Conservative former party leader Sir Iain Duncan Smith warned losing the trust of victims of modern slavery could lead to the UK becoming a "soft touch on trafficking".

He also called for evidence of false claims to be published and suggested changes to the Bill. Sir Iain said: "The more we help them, the more they give evidence, the more of the traffickers we catch, the more get closed down, and probably fewer people then come across ... this is all part of a circle of trust and identification and final prosecution." Conservative former minister Sir John Hayes said amendments tabled by colleagues to "make the Bill work" are needed, including proposals to block courts from ordering individuals to be returned to the UK.

He said: "The Bill must work.

"The British people are at the end of their tether, tired of a liberal establishment which is blinded by its own prejudices, which seems oblivious of the needs of working-class Britons, ever more indulgent towards economic migrants or anyone else that comes from abroad for that matter."