British military experts are advising Saudi forces but the MoD insists they are only ensuring that rules of war are complied with.
British military experts have joined Saudi Arabia's military campaign against rebels in Yemen, provoking renewed calls from human rights groups for a total review of British policy towards the fundamentalist kingdom.
At least 10,000 Yemenis have died in the civil war that is being fought as a proxy conflict between Saudi Arabia and Iran.
Now it appears that Britain, already a massive source of weapons and bombs to the Saudi Kingdom, is helping in more direct ways.
Sky sources have confirmed that six experts are working with Saudi targeteers who select locations for attack.
The Ministry of Defence (MoD) in London insists they are not part of any direct operations but are training the Saudis to comply with the international rules of war.
But Human Rights Watch has produced detailed investigations that it says reveal some 30 examples of Saudi coalition breach of international rules of war.
The report, published in December, calls for investigations into the incidents which may constitute war crimes, according to David Mepham, director of Human Rights Watch UK.
He said: "At a time when the Saudis and other members of the Gulf coalition are committing multiple violations of the laws of war in Yemen - we've documented that.
"Human Rights Watch has put out numerous reports about what the Saudis are up to in Yemen - that the British are working hand in glove with the Saudis, helping them, enhancing their capacity to prosecute this war that has led to the death of so many civilians. I think it's deeply regrettable and unacceptable."
Tory MP and former secretary of state for international development Andrew Mitchell has been critical of the Government’s policy of supplying aid to the victims of the Yemeni war and arms to Saudi Arabia while it’s fighting there.
He said he felt British training to avoid civilian casualties would be positive - but added a caution.
"There is no hiding the fact that this is an uncomfortable position for the British Government because one limb of it is desperately trying to save lives, ensure that fuel gets in, ensure that food and medicines get in, and the other arm of government is engaged in prosecuting a ferocious war which is inevitably doing great damage to innocent civilians," said Mr Mitchell.
Britain has agreed contracts worth some £5.6bn in arms exports over the last five years according to arms sales monitoring agencies. It also has a long standing commitment to training Saudi forces.
But with the additional personnel attached to the Yemen campaign it risks being dragged into a regional sectarian war which is pitting Iranian and Saudi proxies against each other in Syria and the Yemen.
Diane Abbott, Shadow International Development Secretary, told Sky News: "It is one thing to negotiate with people, it is another thing to be complacent in human rights offences.
"How sure are you that that is going on, because what Sam Kiley has revealed in his report is that there are six British military helping the Saudis with their targeting, but specifically helping them to make sure they comply with international agreements.
"We need to know more about the export licences, Saudi is a huge purchaser of British arms."
Ministers refused to comment on the Sky News revelations.
A MoD statement said: "UK military personnel are not directly involved in Coalition operations, but are supporting Saudi forces through pre-existing arrangements and additional liaison officers in Saudi headquarters.
"We operate one of the most rigorous and transparent arms export control regimes in the world with each licence application assessed on a case by case basis, taking account of all relevant information, to ensure compliance with our legal obligations.
"No licence is issued if it does not meet these requirements."
