A father-of-three who was found with a microscopic speck of cannabis stuck to the bottom of one of his shoes has been sentenced to four years in a Dubai prison.

Keith Brown, a council youth development officer, was travelling through the United Arab Emirates on his way back to England when he was stopped as he walked through Dubai's main airport.

A search by customs officials uncovered a speck of cannabis weighing just 0.003g - so small it would be invisible to the naked eye and weighing less than a grain of sugar - on the tread of one of his shoes.

Dubai International Airport is a major hub for the Middle East and thousands of Britons pass through it every year to holiday in the glamorous beach and shopping haven.

But many of those tourists and business travellers are likely to be unaware of the strict zero-tolerance drugs policy in the UAE.

One man has even been jailed for possession of three poppy seeds left over from a bread roll he ate at Heathrow Airport. Painkiller codeine is also banned.

If suspicious of a traveller, customs officials can use high-tech equipment to uncover even the slightest trace of drugs.

Mr Brown was detained and arrested in September last year and has been held in a cell with three other men in the city prison ever since.

This week the youth worker, who has two young children and a partner at home in Smethwick, West Midlands, was sentenced to four years in prison.

A 25-year-old Briton who was found with a similar speck in one pocket as he arrived on holiday has been awaiting sentence since November.

Meanwhile a Big Brother TV executive has so far been held without charge for five days after being arrested for possessing the health supplement melatonin.

The authorities claim to have discovered 0.01g of hashish in his luggage.

Last night Mr Brown's brother Lee said his case "defied belief".

"For that sort of amount common sense should prevail, from where it was found it was obviously something that had been crushed on the floor - it could have come from anywhere."

Rastafarian Mr Brown had been returning from a short trip to Ethiopia, where one of his children lives and where he owns property.

He was travelling with his partner Imani, who was also stopped and detained for more than a week.

Normally he flew direct to and from the UK, but decided to stop off in Dubai.

"He was incensed when he called me," said driving instructor Lee, 57. "It would be funny if the circumstances weren't so unpleasant.

"Bugs are crawling out of his mattress when he's sleeping. His family are frantic with worry and can't call him."

Last night campaign group Fair Trials International advised visitors to Dubai and Abu Dhabi to "take extreme caution".

Chief Executive Catherine Wolthuizen said: "We have seen a steep increase in such cases over the last 18 months.

"Customs authorities are using highly sensitive new equipment to conduct extremely thorough searches on travellers and if they find any amount - no matter how minute - it will be enough to attract a mandatory four-year prison sentence."

Mrs Wolthuizen added: "We even have reports of the imprisonment of a Swiss man for 'possession' of three poppy seeds on his clothing after he ate a bread roll at Heathrow.

Cat Le-Huy

Held: A campaign is underway to secure the release of Cat Le-Huy from a Dubai jail

"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."

Only two months after Mr Brown was stopped economics graduate Robert Dalton was detained in almost identical circumstances.

Mr Dalton, from Gravesend, on Kent was with two friends when he was stopped and asked to empty his pockets.

Officials found 0.03g of cannabis in a small amount of fluff. He is currently on trial and if convicted, is likely receive a four-year prison sentence.

Last night his brother Peter, 26, told how it took 24 hours to find out why he had been stopped.

"As we understand, the amount of cannabis was barely visible to the human eye and was at the bottom of the pocket of an old pair of jeans.

"He's not a drug user, but he goes clubbing and the speck was so small."

Last week Cat Le-Huy, a London-based German national, was arrested on arrival at the airport.

Mr Le-Huy, 31, head of technology with Big Brother production company Endemol, was arrested on suspicion of possessing illegal drugs after customs officers found melatonin, a health supplement used for jet lag available over the counter both in Dubai and in the US.

Authorities also claim they discovered fragments in one of his bags which they believe to be hashish. Fair Trials International said the amount was 0.01g.

So don't go there.

Sue