The information, released under the Freedom of Information Act, shows that one hospital is spending up to £1m a year on dialysis for nearly 40 non-British residents; another has placed two asylum seekers on its waiting list for transplants and a third has recovered only 2% of its costs from overseas patients.

Doctors and patient groups say the NHS is struggling to provide kidney dialysis for British patients and is ill-equipped to cope with the extra demand.

They warned of an acute moral dilemma as doctors balance their overriding responsibility to help those in greatest need with the fact that the patient may not be legally entitled to treatment.

There are fears some foreign patients, so-called “health tourists”, may travel to Britain to take advantage of free NHS care.

Dr Jonathan Kwan, head of renal services at Epsom and St Helier hospitals trust in Surrey, said: “Non-UK residents are putting pressure on the system, which is already under too much pressure.”

Kwan said British patients risked losing out to those from overseas who needed treatment more urgently. “Patients waiting for dialysis may be displaced by a clinically urgent case. Doctors try to prioritise the urgent cases irrespective of residency status.”

There are a record 6,000 patients on the kidney transplant waiting list, with about 400 dying each year in Britain before an organ becomes available. Patient groups say some British sufferers are forced by a lack of dialysis machines to receive treatment at night.

While most health tourists seek one-off operations, patients suffering from kidney failure require dialysis three times a week for life unless given a transplant.

According to the figures, Barts and The London NHS Trust, which covers two of the largest hospitals in the capital, is providing 37 non-UK residents and an extra 14 asylum seekers with dialysis.

Two asylum seekers are on the kidney transplant waiting list at the Royal Berkshire NHS Foundation Trust in Reading.

Although trusts may try to invoice non-UK residents for treatment, they usually recover only a fraction of the cost.

Asylum seekers are entitled to free treatment while their case is being considered.

In the last financial year St George’s hospital in south London spent about £100,000 on dialysis for overseas patients but has recovered only £2,100.

Timothy Statham, chief executive of The National Kidney Federation, said: “Capacity is at breaking point,” he said. “We have very ill British] patients needing to dialyse through the night because there is not sufficient capacity. Some patients may come from abroad because dialysis was not available in their country. We seem to be offering a world health service.”

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