A 23-year-old British citizen has claimed he has been left to rot in a foreign prison where he has been subjected to "torture and abuse".

Sharjeel Chaudary, from Elbourne Road, Tooting, alleges he was made to stand in a Dubai jailyard for three hours in scorching 48 degree heat - while being denied food and water.

And after speaking out, Mr Chaudary said prison guards have warned him against making any formal complaint - or he may face retaliation.

His claims emerged this month in a desperate plea for help sent to his sister Mahwash, in which he said he was "really scared for his life".

A spokeswoman for the Foreign Office told the Wandsworth Guardian staff were aware of the allegations, and had asked the colonel of Dubai's Central Jail to investigate them.

Mr Chaudary, who is currently three months into a three year prison sentence, was jailed after being found guilty of failing to repay a 205,000 United Arab Emirates dirhams debt - equivalent to about £34,000.

However, Mr Chaudary insists he does not owe the money, and said he was found guilty without ever being given the chance to defend himself.

The former Graveney School pupil began working in Dubai for a recruitment company in July, 2009. After several months he moved to a different firm but, according to Mr Chaudary, his previous employer refused to return his passport until he repaid a commission given to him when he began his employment.

Mr Chaudary paid back 75,000 United Arab Emirates dirhams (about £12,500) and agreed to pay the remainder as soon as he earned it. However, unknown to Mr Chaudary, his previous employer took the matter to court and after six hearings - none of which Mr Chaudary claims to have been told about - won the £34,000 claim.

Mr Chaudary was hauled into court and jailed after a seventh hearing, lasting only minutes.

In the letter to his sister in which he detailed his treatment, he wrote: "It has been four days now since that day and I have not left my cell or wing.

"Also, no one from the UK consulate has called or come to see me even though I was promised.

"I am genuinely concerned about my welfare and treatment especially after the torture and abuse I suffered and reported. I hope your help arrives soon and this nightmare ends and I can come home and be with my family."

Mrs Chaudary said: "We are really concerned for his safety and his well being. His case in Dubai was a disgrace.

"I am desperate to help but don’t know what to do."

Tooting MP Sadiq Khan said: "I am very concerned to hear of another local resident detained in Dubai.

"I am making enquiries with the Foreign secretary to ensure that all that can be done to help Mr Chaudary is being done."

The Foreign Office spokeswoman said: "We are aware of Mr Chaudary’s claims of mistreatment in jail in Dubai. Staff from the British Embassy in Dubai have visited Mr Chaudary.

"We take all allegations of mistreatment very seriously and have already raised the issue directly with the colonel of the jail. He has committed to investigating them urgently."

The United Arab Emirates Embassy declined to comment.