The remarkable story of a postman who emigrated to Thailand only to land himself in one of the country’s most notorious prisons will be told on our TV screens tomorrow night.

Jimmy Kelly was living in Watford with his parents when he was suddenly given a £33,000 redundancy payout.

It was a welcome surprise for Mr Kelly, who ‘hated’ his job, and he seized on the opportunity by heading out to Asia to fulfil a lifelong dream of opening his own bar.

But his dream soon turned into a nightmare, as will be explained in the show Banged Up Abroad.

Harrow Times:

Jimmy Kelly, pictured, tells his story of his dream which turned into a nightmare in Thailand. Credit: Nat Geo

Mr Kelly, who was in his late forties, had his business brain on when he jetted out but soon he became distracted, squandering much of his new found wealth on partying.

He did open a bar, Jimmy Chang’s and it was a success, but he became obsessed with Thailand’s party scene and was soon taking crystal meth, which triggered a downward spiral for the former postman.

Speaking on the show, Mr Kelly said: “I was loving my life. I didn’t feel like Jimmy the postman.”

But having his bar in the Koh Samui red light district had its consequences and soon Mr Kelly began dealing drugs and pimping out prostitutes, which raked him in thousands of pounds.

Now 51, he recalled: “It was only-low key but I became greedy. In hindsight it was a terrible idea.”

Watch a clip from tonight's episode of Banged Up Abroad (reenactment)

He was soon selling 200 grams of crystal meth but realised he was the only westerner in the area in the drugs trade.

Then suddenly he was busted, caught red-handed by Thai police in an undercover operation. He had hooked up with a woman, who turned out to be a police officer, and when officers swooped, the game was up.

He was sent to Koh Samui District Prison where he served two years, during which he lost three teeth, before serving the rest of his sentence at Wandsworth Prison in London.

He was released in 2014 after serving a total of three years and four months.

Remembering his time in prison in Thailand, Mr Kelly said: “I'd read horror stories about Thai but prisons I never thought in my right mind I'd end up in one.

“I couldn't believe what I was walking into. The first time I saw my cell I couldn't believe the size of it. It was like 20 ft by 20ft and there was 30 of us.

“It was bad enough trying to stand up, let alone lying down to sleep. There was a squat toilet in the corner of the room. It stank as well.”

During the show, Mr Kelly, who now lives in England, describes his regret at how his life unfolded in Thailand.

Banged Up Abroad airs tonight at 9pm on the National Geographic channel.