An investigation into scammers found that British men were being offered up to £10,000 to pretend to be fathers.
According to an investigation carried out by the BBC, some of the scammers are using Facebook to offer their services and say they've helped thousands of women remain in the UK.
BBC Newsnight sent in an undercover researcher pretending to be a pregnant Vietnamese woman who was in the UK illegally.
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She was told by the visa scammers that they could connect her with multiple British men who would pose as her baby's father and be listed on their birth certificate
The researcher was told that for £11,000, she would receive the 'full package' and was introduced to a man named Andrew who would get £8,000 of that to pretend to be the baby's father.
The BBC investigation contacted other scammers who said they'd pay '£10,000 for the dad' and take £300 for themselves and claimed to have provided the service to thousands of women.
Basically, if a British national is the father then the child gets UK citizenship and their mother would be able to apply for a family visa and the right to remain in Britain.
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If a person has been living in the UK for five years they can then apply for indefinite leave to remain, which means you can be a resident in Britain for as long as you like and there's no need to keep extending a visa.
Once a person has had indefinite leave to remain for 12 months they can apply for British citizenship if they so desire, though there are tests which need to be passed in that case and it costs money.
The Home Office told the BBC they have 'measures in place' to detect fraud and false birth certificates, saying that sometimes they ask for more evidence than just a birth certificate.
Deliberately giving false information for a birth certificate is a criminal offence in the UK and could result in a person receiving a prison sentence.
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Further investigation from the BBC found that last year there were 4,860 family visas given to 'other dependents', which includes people who are applying to stay in the UK because they are parents of children with British citizenship.
Newsnight's investigation found 'dozens of posts' on Facebook from accounts saying they'd be able to pose as fake fathers and others from women trying to get in contact with one of these men.
One of the women they spoke to said she'd paid a man £9,000 to pose as her baby's father and that she only met him three times, while another said she paid £10,000 to a man and discovered he didn't have British citizenship after his name had gone on her child's birth certificate.
Facebook's parent company Meta said that using their social media site to commit birth certificate fraud is not allowed and they will keep removing content where it's happening.
Joe Harker