Britain is training Saudi Arabia's national guard - the elite security force deployed during recent protests in Bahrain - in public order enforcement and the use of sniper rifles.
The news has outraged human rights groups, which point out that the British Foreign Office recognises that the kingdom's human rights record is "a major concern".
In response to questions under the Freedom of Information Act, the Ministry of Defence has confirmed that British personnel regularly run courses for the guard in "weapons, fieldcraft and general military skills training, as well as incident handling, bomb disposal, search, public order and sniper training".
The courses are organised through the British military mission to the Saudi national guard, an obscure unit that consists of 11 British Army personnel commanded by a brigadier.
The ministry's response reveals that Britain sends up to 20 training teams to the kingdom a year. Saudi Arabia pays the bill.
Bahrain's royal family used 1200 Saudi troops to help put down demonstrations in March. At the time Britain expressed concern about reports of human rights abuses by the troops.
"Britain's important role in training the Saudi Arabian national guard in internal security over many years has enabled them to develop tactics to help suppress the popular uprising in Bahrain," said Nicholas Gilby of the Campaign Against Arms Trade.
Analysts believe the Saudi royal family is desperate to shore up its position in the region by preserving regimes in the Gulf that will help check the increasing power of Iran.
"Last year we raised concerns that the Saudis had been using UK-supplied and UK-maintained arms in secret attacks in Yemen that left scores of Yemeni civilians dead," said Oliver Sprague, director of Amnesty International's UK Arms Programme.
Defence Minister Nick Harvey confirmed to Parliament last week that British armed forces provided training to the Saudi national guard.
The confirmation that this training is focused on maintaining public order is potentially embarrassing for the Government. Coming at the end of a week in which the G8 summit approved funding for countries embracing democracy in the wake of the Arab Spring, it has led to accusations that the Government's foreign policy is in conflict with itself.
Jonathan Edwards, a Welsh nationalist MP who has tabled parliamentary questions to the Defence Ministry about its links to Saudi Arabia, said he found it hard to understand why Britain was training troops for "repressive undemocratic regimes".
The ministry's response was made in 2006, but when questioned last week it confirmed Britain had been providing training for the guard to improve their "internal security and counter-terrorism" capabilities since 1964.
The guard was set up by the Saudi royal family because it feared the army would not support it in a popular uprising.