Cataracts occur when the lens in the eye becomes cloudy, causing problems with reading, writing and general vision, which gradually get worse (stock photo)

Health tourists are jumping the queue ahead of NHS patients for life-changing cataract operations, an investigation has revealed.

At least 300 foreign patients flying in from countries including Nigeria and Zimbabwe have been offered surgery before British taxpayers because their condition is deemed a priority.

The treatment costs the NHS up to £2,500 a time including translation costs but many patients return home and never pay it back.

Yet they are being fast-tracked by doctors as their condition is deemed very complex and urgent, leading to lengthy delays for British patients.

Cataract surgery is the most common treatment on the NHS and 300,000 operations are performed a year, mostly on the elderly.

Yet it is being heavily rationed due to financial pressures. Figures have shown that at least half of health trusts currently ration cataract surgery and some patients have been told their vision is 'too good' even though they cannot read or write.

Some areas including parts of Greater Manchester have average waiting times of 222 days – nearly eight months – while others will now only do one eye at a time.

Cataracts occur when the lens in the eye becomes cloudy, causing problems with reading, writing and general vision, which gradually get worse. But they can be easily treated by a simple 30-minute operation to remove the affected lens and replace it with a plastic implant.

Charities have warned, however, that thousands of patients are gradually losing their sight because NHS trusts are refusing to carry out surgery.

The Daily Mail used the Freedom of Information Act to ask all 150 hospital trusts in England a series of questions about overseas patients. The replies show that in the past two years 849 overseas patients were given cataract surgery on the NHS even though they were not eligible for free care.

They included 283 who were fast-tracked to the front of the queue because doctors deemed their condition to be more urgent than others already waiting.

Only 77 trusts managed to reply to any of our questions so the true scale of the abuse is likely to be far higher. Thirteen admitted they never recovered the full costs from the patients.

Professor J Meirion Thomas, a former cancer surgeon at the Royal Marsden Hospital in London, said: 'This investigation proves again that health tourism is flourishing in the face of the feeble efforts of the Department of Health.

'Why should patients who are not eligible for free NHS care be allowed treatment at a rock-bottom price?'

Foreign patients have been offered life-changing cataract operations ahead of British taxpayers because their condition is deemed a priority

He said government research showed that 84 per cent of health tourists never paid their debts.

Conservative MP Peter Bone said: 'We really have to have a system which puts British people first.' Andrew Percy, another Tory MP, said: 'The NHS is facing extreme pressures and its unacceptable that money is being spent on treatment for people that are ineligible.'

Last August the Daily Mail Investigations Unit revealed that the vast scale of health tourism in the NHS was being covered up by hospital bosses.

NHS whistleblowers said they are told to disguise the true number abusing the health service by bosses who 'don't want to know' – and are branded racist if they speak out.

By law, only patients who are 'ordinarily resident' in the UK – and have lived here for at least six months – are eligible for free treatment, operations and scans. But lifesaving procedures, maternity care, A&E treatment and GP services are free for all.

Ministers have repeatedly promised to crack down on health tourism amid accusations that the NHS is too lax compared with other EU countries.

They twice unveiled proposals to start charging foreign patients in A&E although they are still 'consulting' on the plans and there is no clear start date.

I HAD TO WAIT FOR TWO YEARS, SAYS 83-YEAR-OLD GRANDMOTHER Bernice Cowles (pictured) waited two years for cataract treatment on the NHS Bernice Cowles waited two years for cataract treatment on the NHS after being told her failing sight was too good. In 2013, the 83-year-old grandmother, pictured, was caring full-time for her husband William, who has since died, and struggled to read the small writing on his prescriptions without a magnifying glass. She was referred for an operation in April 2015 to repair her left eye, which was more severely affected. But this was only after a routine sight test revealed her vision was so poor that it met the NHS's strict eligibility criteria. Mrs Cowles, from West Horndon, Essex, said the operation was 'very successful' – and she hoped to have the other eye operated on soon. Advertisement

Yet most other countries in the EU demand to see patients' identity cards or passports before offering them treatment.

The Mail was alerted to the problem by a whistleblower from a hospital whose role is to charge foreign patients.

She said many patients, mainly from Nigeria and Zimbabwe, are brought in by relatives living here. The relatives then take them for eye tests by opticians, who refer them to hospital, where doctors carry out cataract surgery immediately. But they do not demand money beforehand.

The whistleblower said that between five and 15 overseas patients arrive at her hospital a week needing cataract treatment. 'We rarely get the money back,' she said. 'They tend to need very complex procedures. We have to use a translation service as well and it's a huge cost.'