Government departments are intensifying efforts to win lucrative public contracts in Saudi Arabia, despite a growing human rights row that led the ministry of justice to pull out of a £6m prison contract in the kingdom last week.

Documents seen by the Observer show the government identifying Saudi Arabia as a “priority market” and encouraging UK businesses to bid for contracts in health, security, defence and justice.

“It’s becoming increasingly clear that ministers are bent on ever-closer ties with the world’s most notorious human rights abusers,” said Maya Foa, director of Reprieve’s death penalty team. “Ministers must urgently come clean about the true extent of our agreements with Saudi Arabia and other repressive regimes.”

The UK’s increasingly close relationship with Saudi Arabia – which observes its own version of sharia law, under which capital and corporal punishment are common – is under scrutiny because of the imminent beheading of two young Saudis. Ali al-Nimr and Dawoud al-Marhoon were both 17 when they were arrested at protests in 2012 and tortured into confessions, their lawyers say. France, Germany, the US and the UK have raised concerns about the sentences but this has not stopped Whitehall officials from quietly promoting UK interests in the kingdom – while refusing to make public the human rights concerns they have to consider before approving more controversial business deals there. Several of the most important Saudi contracts were concluded under the obscurely named Overseas Security and Justice Assistance (OSJA) policy, which is meant to ensure that the UK’s security and justice activities are “consistent with a foreign policy based on British values, including human rights”. Foreign Office lawyers have gone to court to prevent the policy being made public.

The Labour leader, Jeremy Corbyn, has written to David Cameron asking him to commit to an independent review of the use of the OSJA process.

“By operating under a veil of secrecy, we risk making the OSJA process appear to be little more than a rubber-stamping exercise, enabling the UK to be complicit in gross human rights abuses,” Corbyn writes.

The UK has licensed £4bn of arms sales to the Saudis since the Conservatives came to power in 2010, according to research by Campaign Against Arms Trade. Around 240 ministry of defence civil servants and military personnel work in the UK and Saudi Arabia to support the contracts, which will next year include delivery of 22 Hawk jets in a deal worth £1.6bn. And research by the Stockholm International Peace Research Institute shows that the UK is now the kingdom’s largest arms supplier, responsible for 36% of all Saudi arms imports.

UK business want to capitalise on the fragile situation in the Middle East. A 2013 document, written by an official at UK Trade and Investment, the body charged with promoting business interests,, outlines how the region’s “global policing and security market has ballooned”. Freedom of information requests show that the UK Trade and Investment Defence and Security Organisation (UKTI) is courting the Saudis and that civil servants met Saudi military delegations at the UK’s Security and Policing arms fair this year and last summer at the Farnborough airshow. Civil servants were also due to meet Saudi representatives at the major arms expo in London’s Docklands last month, just as the regime upheld a ruling that al-Nimr was to be executed and his body crucified and left in public view for three days.

The UKTI is offering grants to support businesses, including those selling security equipment, to take part in overseas exhibitions aimed at specific emerging markets, notably Saudi Arabia.

However, human rights groups are asking why the UK is intent on selling arms and security equipment to a repressive regime when it has withdrawn from the prisons contract.

More than 100 people have been executed in the first six months of this year in Saudi Arabia. Andrew Smith, of the Campaign Against Arms Trade, said: “The Saudi regime has an appalling human rights record, yet it remains the world’s largest buyer of UK weapons. How many more people will be tortured and killed before the UK government finally says enough is enough?”

It was concerns about Nimr and Karl Andree, 74, a UK citizen sentenced to 350 lashes for possession of alcohol, that persuaded the justice secretary, Michael Gove, to pull out of the prisons contract, , sparking a row with the foreign secretary Philip iHammond, who reportedly accused him of naivety.

There are questions about other UK-Saudi deals. One is with the UK’s National College of Policing, which signed a secret memorandum of understanding to help modernise the Saudi ministry of the interior. The UK also signed a 2011 memorandum of understanding with the regime on healthcare.

“It seems ironic for the UK to be working on healthcare with the Saudi regime at the same time as selling them the means to suppress and kill their own people,” Smith said. According to human rights groups, more than 100 people have been executed in the first six months of this year in Saudi Arabia. Reprieve claims two Pakistani men convicted in the Saudi courts are due to be beheaded very soon. According to their lawyers, Muhammad Irfan and Safeer Ahmad, from Pakistan, were taken to the kingdom by men posing as “employment agents”, and were led to believe that they would find work there. The men’s lawyers say they were forced to bring drugs into the country and were arrested by Saudi police on arrival. Both were sentenced to beheading. It is believed that the sentences have now been upheld, and that they now face imminent execution.