The UK Government has told supporters of a British woman jailed for heroin smuggling in Thailand that it cannot offer formal support to her plea for clemency.

However, Foreign Office Minister Peter Hain revealed that Thai King Bhumibol's decision on a royal pardon for Sandra Gregory was expected later this year.

In 1993, the former teacher was jailed for 25 years for attempting to take heroin out of Thailand.

She was arrested at Bangkok Airport in 1993 as she was about to board a Tokyo-bound plane but alleged that the near 100 grammes of heroin found on her had been given to her by her then boyfriend Robert Lock.

He was acquitted while she was jailed for the minimum mandatory sentence.

The 35-year-old served four years in what is nicknamed the Bangkok Hilton before being repatriated to Britain to serve out the rest of her sentence which had been reduced to 22 years as part of a general Thai amnesty.

Her parents, who live in Aberdeenshire, have long campaigned for her release and the Foreign Office was urged to step up pressure on the Thai Government to review her sentence.

The couple met local MP Malcolm Bruce last week and, during a short House of Commons debate on Monday, Mr Bruce called on the government to act.

Opening the debate, he warned the government that it risked "unfairness and inconsistency" by not supporting her appeal.

Mr Bruce, the Liberal Democrat MP for Gordon, said Ms Gregory was serving the third longest sentence of any British woman - behind mass murderers Rosemary West and Myra Hindley.

Mr Bruce said: "Sandra was not motivated by greed, she was not planning to sell the drug or realise its value, she was accepting payment for acting as what is known in the trade as a 'mule'.

"It was not, as some people have suggested, an act of greed - it was an act of irrational desperation by a sick and homesick young woman."

Amoebic dysentery

Mr Bruce said Ms Gregory had accepted �1,000 payment to buy a flight home while suffering from dengue fever and amoebic dysentery.

"Neither Sandra, nor her parents Stan and Doreen deny an offence was committed or that Sandra should have been punished. The issue is entirely one of proportionality," he said.

Mr Hain said the British Embassy in Bangkok was told on 6 January that a decision on Ms Gregory's royal pardon petition was likely to be known in the middle of this year.

He told the house: "While we sympathise with Sandra's family and anyone who is separated from their loved ones, the compassionate circumstances do not exist which would warrant the government formally supporting her plea to the Thai authorities for early release, but that does not mean we have not made representations.

"I'm sure that the Thai authorities will take very careful note of this debate."

Mr Hain added: "British nationals detained abroad are subject to local jurisdiction wherever they commit their crimes.

"We have to respect the right of other countries to decide their own sentencing guidelines. Indeed, we expect the same respect ourselves.