The Government is refusing to release 38-year-old papers shedding light on Britain’s relationship with the authoritarian regime in Bahrain, amid suggestions that it is protecting a deal on a new Royal Navy base in the Gulf country.

Campaigners asked the Information Rights Tribunal to intervene and force the Foreign Office (FCO) to release the full text of a 1977 document detailing the conversation between British officials and Ian Henderson, a British military officer who ran the police force in the Sunni-ruled state for 30 years.

Henderson, who died two years ago, was dubbed the “Butcher of Bahrain” after allegations that he was complicit in the ransacking of villages, the sadistic sexual abuse of Shia prisoners and the use of power drills to maim them.

The document should be available under the 30-year-rule controlling the release of government papers, but Marc Jones, an academic and a member of the Bahrain Watch human rights group, says the FCO has refused to release it despite repeated requests.

Instead, only a heavily redacted version has been released. Mr Jones believes the full document is highly critical of the Khalifa family, which rules the state, and is being held back to save them “embarrassment” and avoid jeopardising a deal for a new Royal Navy base.

He said: “My appeal is reflecting public concern that the British Government has insulated the Government of Bahrain from criticism of serious human rights abuses including torture, and may have concealed evidence of serious wrong-doing. In the unredacted information, there are indications that the withheld information could contain information important in understanding why the British-led Bahrain police force had a tendency towards deviance and torture.”

In heavily redacted written evidence submitted to the tribunal, Edward Oakden, a senior FCO diplomat and former ambassador to the United Arab Emirates, said the document should not to be released, citing the base as vital for improving “operational effectiveness in a volatile region” and adding that Bahrain is a “generous host” to the Navy and the RAF.

The tribunal is expected to reach a verdict on the appeal within four months. Meanwhile, Amnesty International has found that the Bahraini regime continues to “curtail freedoms of expression, association and assembly” and that its security forces have used “excessive force to disperse protests” killing at least two people in the past year.

The redacted document is believed to detail Henderson’s verdict on Bahraini security officials, potentially including members of the Khalifa family. His career was closely linked with the ruling family, including the Prime Minister Khalifa bin Salman, who has run the country since 1970.

Mr Jones said: “By attempting to shield information that highlights the dependence of the Khalifa on the British, the public are being deprived of important information of historic British complicity in human rights violations.”

Henderson was installed as head of security in Bahrain in 1966, when the country was still a British protectorate. As a colonial officer he had helped suppress the Mau Mau insurgency in Kenya, and when Bahrain declared independence in 1971, Bin Salman kept him as head of the country’s intelligence service.