Dubai is popular among tourists and businesses

Fair Trials International said arrests were being made over tiny quantities of drugs and over-the-counter medicines.

British tourist Keith Brown was sentenced to four years in prison after Dubai customs officers found a 0.003g trace of cannabis stuck to his shoe.

Fair Trials, a legal charity, said it has seen a steep rise in such cases.

Golden beaches

Possession of painkillers like codeine and some cold and flu medication could result in a mandatory four-year prison sentence, Fair Trials International said.

In one of the most extreme cases, it reported a man being held after poppy seeds from a bread roll were found on his clothes.

In recent years, chic hotels, skyscrapers and golden beaches have turned Dubai and Abu Dhabi into popular tourist destinations.

Many have no idea what risks they're taking or their vulnerability to this very strict approach

Catherine Wolthuizen, Fair Trials International chief executive

Businesses too have flocked to the UAE, which promises a high standard of living because of its oil wealth.

However, while it is considered one of the most liberal countries in the Gulf, the Muslim country's drugs laws are severe.

Last year, 59 Britons were arrested in the UAE on drugs-related charges, according to the Foreign Office.

HELD IN THE UAE Keith Brown, 43, Middlesex: Four-year jail term for possession of 0.003g of cannabis Robert Dalton, 25, Kent: On trial for alleged possession of 0.03g of cannabis 20-year-old, West Yorkshire: On trial for alleged possession of 0.02g of cannabis Tracy Wilkinson, 45, West Sussex: Held in custody for eight weeks for possession of codeine before release Swiss national: Four-year jail term after poppy seeds found on his clothes Source: Fair Trials International

Catherine Wolthuizen, chief executive of Fair Trials International, said customs authorities were using highly sensitive new equipment to conduct thorough searches on travellers.

"So many people now travel to Dubai and, as we're seeing, many have no idea what risks they're taking or their vulnerability to this very strict approach," she said.

"If they find any amount - no matter how minute - it will be enough to attract a mandatory four-year prison sentence.

"What many travellers may not realise is that they can be deemed to be in possession of such banned substances if they can be detected in their urine or bloodstream, or even in tiny, trace amounts on their person."

Jet-lag tablets

Keith Brown and his wife had been on their way from London to Ethiopia when they were stopped and searched at Dubai airport.

At first customs officers found nothing, but then a roll-up cigarette was spotted caught in the tread of his shoe.

The 43-year-old, from Middlesex, was charged with possession of 0.003g of cannabis and was sentenced to four years in prison.

I suppose there's a sense of disbelief more than anything else

Cat Le-Huy, held in Dubai

British resident Cat Le-Huy was arrested in Dubai for carrying Melatonin jet-lag tablets, which are sold over the counter in the US and Dubai.

Mr Le-Huy told BBC News he was forced to sign a document in Arabic and was refused a translator.

He said once the tablets were proved to be Melatonin, police took what he described as dirt from his bag and said they were now testing it to see if it was cannabis.

Speaking from inside the prison, he said he knew nothing of any drugs in his bag.

"I suppose there's a sense of disbelief more than anything else. I miss my friends and family back in London and I'm also aware of the other stress this is causing to friends and family.

"As far as my welfare, I'm being treated relatively well and I have to go through the system and whatever path that takes, I'll just have to deal with it."

Bread roll

Aside from illegal substances, travellers have also been held for possession of prescription drugs.

Tracy Wilkinson was held in custody for eight weeks before customs officers accepted the codeine she was carrying had been prescribed by her doctor for back pains.

Meanwhile, a Swiss national is serving a four-year jail term after three poppy seeds from a bread roll he ate at Heathrow airport were found on his clothes.

Fair Trials International has published a full list of banned substances on its website.

The Foreign Office is advising all travellers carrying any prescription drugs to take a doctor's letter detailing exactly why they need the medicine and the exact dose.

The UAE Embassy in London said it would not comment at this stage.