A confidential report leaked to the programme revealed the money was used to treat 71 ineligible patients in three months alone last year.

Commenting on the figures, government health policy advisor Ray Rowden said: "These are staggering sums that would buy an awful lot of cataracts for legitimate patients."

But despite the growing problem of so-called health tourism, one London health trust recently advised doctors not to seek proof of entitlement for fear of discriminating against refugees and asylum seekers.

Kola Ashimi comes from Nigeria for NHS treatment

GPs, the gatekeepers to the NHS, could face legal action if they attempt to strike off suspected cheats.

Manchester doctor Ian Burton told Real Story he was threatened with legal action when he tried to remove an Iranian family who registered a growing number of overseas relatives and visitors at their address.

"Our own defence organisation said that if it went to court we'd have lots of bad publicity," he said.

"From that point on we've not policed anything."

In some parts of London up to 80% of GPs have closed their lists to new patients.

But Real Story secretly filmed a Russian journalist who successfully registered with a South London GP, giving a fake address, in the same afternoon that she flew into the capital.

Regular check ups

In Lagos, the programme interviewed Nigerians who not only have British GPs, but come over to the UK whenever they need operations or expensive drugs.

It would be better if we gave aid or drugs to treat these conditions in other countries rather than a health service that is stretched to breaking point Professor Roger Williams

Businessman Kola Ashimi has sickle cell anaemia, and is on long-term medication.

"I travel to England very regulary," he said.

"I go for my business and my checkups. There's no comparison to what it's like out here."

Health tourists are increasingly seen on maternity wards.

At a busy hospital in London's East End, half of all the maternity patients at any one time are from overseas, at an average cost of �1,500 per patient.

Russian Dasha Pushkova tested how easy it was to access the NHS

Overseas patients manager Pauline Lewis said: "They come here from numerous countries very, very pregnant. It's too late for our immigration officers to even consider sending them back."

Another key area of controversy is HIV and AIDS treatment.

2,500 new HIV and AIDS cases came into the UK last year. According to the Institute of Hepatology, these cost an average of �15,000 per patient.

Some AIDS clinics revealed to the programme that up to 80% of patients have lived in the UK for less than a year.

The Institute of Hepatology's Professor Roger Williams said: "It's a phenomenal cost. It would be better if we gave aid or drugs to treat these conditions in other countries rather than a health service that is stretched to breaking point taking all these extra patients with serious diseases."

Real Story: Monday 11 August at 1930 BST on BBC ONE and the Real Story website.