Overseas patients have left the NHS with more than £150million in unpaid bills for treatment, a Daily Mail investigation reveals.

The cash could pay for 6,000 nurses, 22,000 heart bypasses or nearly 5,500 junior doctors.

Two hospitals in London are owed £28million each, including almost £500,000 from one patient alone.

The revelation comes amid a new-found reluctance among frontline staff to chase payments, with doctors' leaders saying their obligation to charge overseas patients is 'racist' and deters vulnerable groups from seeking help.

But Tory MP Philip Davies said: 'It is the National Health Service, not an international health service and it is essential these charges are made for overseas visitors.'

One hospital is still chasing a bill of more than £500,000 from a Nigerian mother who gave birth to quadruplets in 2016. Priscilla, who was 43 at the time, went into labour shortly after landing at Heathrow airport

Freedom of information requests by the Mail found King's College Hospital in south London is owed £28.3million from foreign patients for treatment in the last few years. In east London, Barts Health Trust is chasing £27.8million of unpaid bills, including £467,000 from one patient, whose nationality or identity was not disclosed when questions were asked.

Although London hospitals have the highest debts, 23 NHS organisations across England are owed at least £1million from foreign patients.

In total, responses from 91 hospital trusts show they are owed £149.5million. But the true cost may be many millions more, with around a third of trusts – another 60 – failing to provide details.

In addition, the figures only account for those patients flagged up as an 'overseas visitor' who were charged for their care.

Many others may have had free treatment as staff presumed they were UK residents, or chose to turn a blind eye as part of a new drive from within the service.

Tory MP Philip Davies (pictured) said: 'It is the National Health Service, not an international health service and it is essential these charges are made for overseas visitors'

This is despite tough new guidance issued by the Department of Health at the end of 2017 instructing staff to properly identify overseas visitors by asking for passports and utility bills, and to hand out invoices before starting treatment.

The new rules are strongly opposed by doctors' leaders, including the influential British Medical Association, with some members describing them as racist. One pressure group called Docs Not Cops is actively discouraging staff from handing out bills and urges them to challenge colleagues if they are seen to check patients' passports. Other influential bodies including the Royal College of Midwives and the Royal College of Paediatricians and Child Health have warned the charges will deter vulnerable pregnant women and mothers with sick children from seeking help.

The NHS tries to recover unpaid bills from individuals rather than the countries they are from, unless they are EU citizens.

MPs said the £150million owed by overseas patients could be used to pay for social care, additional frontline staff or vital treatment such as cataract surgery.

Philip Hollobone, Tory MP for Kettering, said: 'Well-paid NHS bosses who fail to charge visitors for using our health service should have action taken against them.

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'That £150million could go a very long way in paying for thousands more doctors, nurses and badly needed healthcare.'

Mr Davies, MP for Shipley, said: 'The BMA are always the first to say the NHS needs more money, and so they can help deliver that by helping to ensure these large sums of money are collected and put back into the NHS.'

By law only patients classed as 'ordinarily resident' in the UK – living here for at least six months and paying taxes – are entitled to free NHS care in hospitals.

As well as King's College and Barts, many other trusts are owed large amounts. Of those which answered a freedom of information request, St George's University Hospitals trust in south London is trying to recoup £8.3million, Chelsea and Westminster Trust is owed £5million, and Epsom and St Helier in Kent £5.5million. A Department of Health and Social Care spokesman said: 'Every taxpayer supports the health service and so it is only right overseas visitors contribute towards their treatment costs.

'All NHS trusts must charge overseas visitors for the care they receive, unless an exemption applies, and to rigorously pursue any outstanding bills. We've made good progress in the last few years, with £1.3billion recovered.'

Premature triplets cost the NHS £500k

One hospital is still chasing a bill of more than £500,000 from a Nigerian mother who gave birth to quadruplets in 2016.

Priscilla, who was 43 at the time, went into labour shortly after landing at Heathrow airport.

She had intended to fly to Chicago to have her babies, but was turned away by US officials who claimed she would be unable to afford the healthcare costs.

Priscilla was taken to Queen Charlotte's and Chelsea Hospital in west London, part of Imperial College Hospital, where she delivered the four babies

Priscilla was returning to Nigeria via London when she started to have contractions three months before her due date. She was taken to Queen Charlotte's and Chelsea Hospital in west London, part of Imperial College Hospital, where she delivered the four babies.

Tragically, two died shortly afterwards because they were so premature. The other two, Elijah and Esther, spent weeks on the hospital's neonatal intensive care ward.

Priscilla's case was brought to light by the BBC documentary Hospital. Staff estimate the total bill for her complicated birth and subsequent care of the babies was over £500,000. Her current whereabouts are unknown.