Lee Brown said that his brother Keith, 43, of Smethwick, West Midlands, had suffered a "grave injustice".

Customs officials found 0.003g of the drug - an amount that is invisible to the naked eye and weighs less than a grain of sugar - in his shoe.

The youth development officer was sentenced to four years in prison.

Lee Brown, 57, said: "Keith's distraught and he's angry, he isn't happy.

"To think that something like that has happened to him when he was in transit... we believe it was because he was a Rastafarian that he was singled out."

He said his brother did not know how the drug came to be in the tread of his shoe.

He added: "He could have stepped in it walking along and he got hell for that.

"I think they were hoping to find other things on him. It's hard to put into words how you feel about such a grave injustice."

Dubai, in the United Arab Emirate (UAE), has a zero-tolerance drugs policy.

The legal charity Fair Trials International has now advised visitors to the UAE to "take extreme caution" and "avoid arrest for 'possession' of a controlled substance".

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."

It follows a recent spate of arrests and imprisonment.

The list of banned substances in the UAE includes many products which are available over-the-counter and off-the-shelf in the UK.

These include medications such as codeine, a common ingredient in pain relief and cold-and-flu medication, and the common baking ingredient, poppy seeds.

A comprehensive list of banned pharmaceuticals is available at the Fair Trials Abroad website.