Mann, 51, has been convicted of plotting a coup in Equatorial Guinea

Simon Mann, a former SAS commander, has been sentenced to seven years in jail by a Zimbabwe court for illegally trying to buy weapons of war.

Conservative MP Henry Bellingham, who has known Mann since school, says Zimbabwe's legal system is discredited.

Mann, 51, admitted ordering the weapons, but said they were needed to secure diamond mines in eastern Congo.

'Extraordinary'

Mr Bellingham, the shadow industry minister, says the government should help Mann return to the UK "for the matters to be investigated here".

"I also say any sentence from a court in Zimbabwe, where the whole legal system has been discredited, is something the British Government must take a close interest in," he said.

"Here is a British citizen who had a distinguished army career, and the government should be trying to help him.

"I have known him for a long time. He has always been an adventurer - but a thoroughly professional one."

He said he found it "extraordinary" that someone with Mann's background and experience should go to a country like Zimbabwe to buy weapons, adding that such a move was tantamount to "asking for everything to go badly wrong".

There is a very real problem in countries where nobody gets a fair trial Stephen Jakobi Fair Trials Abroad

Sir Mark Thatcher, son of former Prime Minister Margaret Thatcher and a friend of Mann's, was arrested earlier this month by South African authorities in connection with the same coup.

He was later released on bail, but is to be quizzed by Equatorial Guinea authorities. He denies any involvement.

The director of the human rights group Fair Trials Abroad, Stephen Jakobi, said: "There is a very real problem in countries where nobody gets a fair trial anyway, because they do not observe international standards, and I am afraid we are dealing with one of those countries here."

Prison visits

A Foreign Office spokesman explained Mann had entered Zimbabwe on his South African passport and that South African authorities were providing consular assistance on his request.

He said British embassy staff had visited him in prison and had regularly attended his court appearances.

Mann, who was educated at Eton and later served in the Scots Guards and SAS, is the founder of a security firm which operates in Africa.

He claims the assault rifles, grenades, anti-tank rocket launchers and other weapons he tried to order from Zimbabwe defence industries were going to be used to protect mining operations in troubled eastern Congo.