British Home Secretary Theresa May signed a "memorandum of understanding" with Saudi Arabia's Crown Prince Muhammad bin Nayef during a trip to the kingdom last year.
The government made no mention of the trip at the time, and the mention of the signing of any such deal came later in the year when a UK Foreign Office report vaguely referred to an agreement between the two countries, designed to "modernize the [Saudi] Ministry of the Interior."
However, following a Freedom of Information (FoI) request by the Liberal-Democrat political party, who were in a coalition government with David Cameron's Conservatives at the time, it has been revealed that the bilateral security agreement is far broader than the government has previously noted.
The government has refused to publish the details of the deal, with a letter from the Home Office, seen by UK newspaper the Independent, admitting that it "contains information relating to the UK's security co-operation with Saudi Arabia."
The Home Office said releasing the document "would damage the UK's bilateral relationship" with the Saudi Kingdom, and could inhibit Britain's national security.
'Saudi Deals Should Not Be Done in Secret'
Despite these claims, opposition political parties and human rights activists have demanded that the government release the details of the agreement for parliamentary and public scrutiny.
"Deals with nations like Saudi Arabia should not be done in secret," said the Liberal Democrat leader Tim Farron, in a reference to concerns over Saudi Arabia's treated of human rights.
“Deals with Saudi Arabia should not be done in secret,” said UK's Tim Farron. “It is time to shine a light onto the shady corners."— Fay Moore (@MooreFay) December 23, 2015
"Parliament should be able to hold ministers to account. It is time to shine a light onto the shady corners of our relationship with Saudi Arabia. It is time we stood up for civil liberties, human rights and not turn a blind eye because the House of Saud are our 'allies,' " Farron added.
There have been increasing concerns about the state of Saudi Arabia's judicial system after new laws expanding the definition of terrorism were introduced in February.
Under the measures, anything seen to be "disturbing" to public order or "destabilizing the security of society" was deemed to be terrorism.
The anti-terrorism laws were extended further in March, with anyone "calling for atheist thought" seen to be "contacting any groups or individuals opposed to the Kingdom", as well as "seeking to disrupt national unity" by calling for protests at risk of being charged with terrorism offences, which are punishable by death.
UK Urged to Come Clean on 'Murky Deal'
The pressure on the UK to backtrack on its relationship with Saudi Arabia resulted in the government announcing it was canceling an US$8.8 million (£5.9m) bid to service the kingdom's prison system.
Amnesty International UK Director Kate Allen said the public needed to know the details of this "murky deal."
"We'd like to know what efforts are being made by UK officials to challenge and prevent abuses in Saudi Arabia's highly abusive justice system?" she said.
"This murky MoU [memorandum of understanding] deal was set up shortly after the Saudi Interior Ministry was granted draconian new powers to hold and interrogate terrorism suspects without a lawyer for 90 days. Have Theresa May's officials ever asked their counterparts to scale back on these excessive powers?"
Cameron should stop quoting other Countries breaches of 'Human Rights' when UK Government and Royalty openly support barbaric Saudi régime.— Dewi Smith-Johns (@DewiSmith_Johns) December 23, 2015
"The UK already has a track record of selling vast quantities of arms to Saudi Arabia while remaining markedly reluctant to publicly criticize Riyadh for its atrocious human rights record," Allen said.