One of the largest hospitals in the country is chasing a bill of more than £500,000 from a Nigerian woman who gave birth to quadruplets.

The 43-year-old, named only as Priscilla, went into labour three months early shortly after landing at Heathrow airport in November.

She had intended to give birth to the babies in Chicago, in the US, where she has family – but was turned away by border officials upon arrival.

They claimed that although she had a visa, she did not have required documents from a hospital stating that she had the money to pay for the birth.

Health tourist? A 43 year-old Lagos native, known as Priscilla, is the subject of this week's BBC2 documentary Hospital after racking-up a £500,000 maternity bill

Priscilla, pictured, said she 'would never earn' enough to pay the bill for her treatment 'if she worked every day in her life'

Priscilla, a healthcare worker, said she was returning to Nigeria via London when she started having contractions.

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

One sadly died shortly after birth while another, a girl named Deborah, passed away on Saturday. The other two, Elijah and Esther, are still being treated on the hospital’s neonatal intensive care ward.

Staff estimate that the total bill for the highly complex birth and the care of the babies is already more than £500,000.

Pictured: One of Priscilla's children. She collapsed while on a stop-over in London and was rushed to hospital where she gave birth

Hospital overseas visitor manager Terry Facey said the cost to Priscilla would be huge and estimated intensive care would cost £20,000 per week per child

The cost of treating one baby in neonatal intensive care is £20,000 a week.

Priscilla is currently staying at a hostel run by a charity and is unable to afford the bill.

Her husband is in Nigeria, and cannot come to Britain to help take care of her as he does not have enough money for a visa or the flight.

Priscilla underwent IVF treatment, which has a high risk of multiple births, as she was struggling to conceive naturally due to her age.

She was told by her doctor to fly to the US to have her babies, as Nigerian hospitals do not have the ‘facilities to cater for the children’.

Her case is revealed tonight in the BBC 2 documentary Hospital, which exposes the pressures of health tourism on the trust.

When first warned of the high treatment costs by overseas visitor manager Terry Facey, she says: ‘I didn’t plan to come here.

‘It’s only money. Money can’t buy life. The last bill I had was £331,000 but – even if I worked every day – I would never earn that much money. My kids are priceless.’

Mr Facey, who has worked at the trust for 12 years trying to collect bills for overseas patients, says: ‘Those invoices are going to be huge ... 20 grand a week for each baby [in intensive care].

Hospital staff said patients can 'frequently disappear into the community', including this Palestinian man, pictured, who had an operation to remove kidney stones and then discharged himself early

A woman from the Philippines, pictured, known only as Sonia, had a heart operation after falling ill visiting her sister in the UK. Both have since flown home and neither can pay

'We will gently push forward and do what we have to do, we’re governed by the rules and regulations. They seem a bit fruitless at times.’

Mr Facey is also chasing a bill of £59,000 from a 56-year-old woman from the Philippines who underwent heart surgery.

Sonia became ill in November while visiting her sister, and had the procedure in the renowned cardiac unit at trust’s Hammersmith hospital.

It's only money. Money can't buy life. The last bill I had was £331,000 but – even if I worked every day – I would never earn that much money. My kids are priceless.

She has since recovered and flown home with her sister, but neither are able to pay the bill.

Sonia said she would have died if she had stayed in the Philippines as she would not have been able to afford the costs of surgery.

She developed sepsis shortly after the operation and was in intensive care for several days, which increased the bill further.

Mr Facey says other patients frequently ‘disappear into the community’ before he has the chance to hand them an invoice.

These have included a Palestinian man who had an operation to remove kidney stones and then discharged himself early.

The patient had claimed he was an asylum seeker and therefore exempt from NHS charges.

But he left the hospital very shortly after the operation, before Mr Facey had been able to check his immigration status with the Home Office.

Debt collector: A member of staff at the hospital clutches a card machine in a bid to reclaim some of the money that's owed to the trust

Danger: The documentary comes after the British Red Cross last week warned hospitals were facing a 'humanitarian crisis'

Mr Facey says: ‘There’s this assumption that its free of charge, but that isn’t the case.

‘Some people might say I’m hard hearted but I wouldn’t accept that at all.

‘I have a capacity to ask a difficult question of someone in very difficult circumstances.

‘You certainly have to distance yourself emotively. Turn your emotions off. Without that, you wouldn’t get the job done.

'It’s a question of informing people that they’re going to be charged on the one hand, but also of informing them that they will be treated appropriately on the other.’

Talking about her bill on the documentary, Priscilla, pictured, said 'It's only money. Money can't buy life'

Mr Facey says the majority of cases involve overseas patients who have fallen ill whilst visiting relatives in the UK.

He says only a few are health tourists deliberately targeting the NHS. A spokesman for Imperial College Healthcare NHS Trust declined to comment.

Last month it emerged that another hospital was chasing a Nigerian mother for a £350,000 bill after she had flown to Britain to give birth to twins.

The woman, who was not identified at the time, had a caesarean at Luton and Dunstable University Hospital, after she was transferred there from another due to pregnancy complications.

Her twins then spent two months in intensive care.

The case was uncovered through a series of freedom of information requests, sent by the Daily Mail to all hospitals in England.

A spokesman confirmed the hospital was owed £348,683 by the mother, who gave birth in 2015.

Luton is one of just three paediatric intensive care units in the East of England, and the trust said it could not refuse treatment ‘if there was a danger to life’.

The responses from 90 hospitals revealed that 13,077 overseas patients were treated in the UK in 2015/16, including 3,066 pregnant women who flew in and had babies.

These women were responsible for some of the highest debts, the figures showed, and a significant number are understood to have come from Nigeria.