HE has won various swimming championships over the years.

But now 16-year-old Nat Armstrong says he feels he has been left on his own by the NHS because of a condition he can’t get treatment funded for.

The City of Oxford Swimming Club member has been diagnosed with candidiasis – a form of yeast infection – which has affected his organs and halted his career in the pool.

And because he’s allergic to medication usually used to treat the condition he has been having a form of alternative treatment that is not funded on the NHS.

He said: “When I’m breathing my chest tightens up. I get so lethargic and just feel so unwell – it impacts on everything I do.”

Lord William’s School pupil Nat, who lives in Thame with his grandparents Bob and Jacqueline, won four Oxfordshire and North Bucks County Championships in various events between 2007 and 2011 and was ranked second in the south east.

In 2011, he had a series of collapses during a training session at Temple Cowley Pools and in competitions.

Doctors at the John Radcliffe Hospital originally thought it was a heart condition and it wasn’t until after a year that he was diagnosed with having an issue with a wide range of food allergies, including proteins and sugars.

He has since been living on a liquid diet and says his health and swimming performances have deteriorated.

He was referred to specialists at the Great Ormond Street Hospital in London and prescribed various drugs, including antibiotics and antifungal medication, but he was allergic to all of them and he was then diagnosed with the condition.

The teenager’s family say he is one of 20 children at the hospital who cannot be treated. In November, they took him to the Breakspear Medical Group clinic in Hemel Hempstead, which tries to desensitise his reactions to allergens so his body can cope with the treatment, which they say costs £1,700 a week.

Nat’s grandfather says the condition, which has infected his kidneys, liver, digestive system and blood, could kill him if it spreads to the brain.

Accountancy business owner Mr Armstrong said: “According to conventional medicine there is nothing we can do so the only thing we can try is to get the body to accept materials that he’s allergic to. We’ve been told there’s a 70 per cent chance of success.”

The clinic’s techniques have not been approved through medical trials so Nat’s GP has not requested NHS funding.

His grandparents have instead funded the treatment for the past three months but may have to sell their house to continue paying for it.

Mr Armstrong said the condition has not affected Nat’s positive personality, adding: “It doesn’t stop him doing things – he’s a remarkable boy and tougher than most people I have come across.

“The main thing we want is for the NHS to support it. In that sense we don’t particularly need or want money if that was to happen.”

Swimming club head coach Amanda Booth, 49, said Nat was now coaching youngsters to keep him involved with the club.

She said: “Nat is a driven and motivated boy as far as swimming is concerned. He puts his all into everything he does. He’s always upbeat and just plods on.”