THE Foreign Office is withholding dozens of files from the National Archives about Britain’s cosy relationship with the brutal Sultan of Brunei, the Star has found.

The revelation comes as Britain’s closest ally in south-east Asia starts stoning people to death for sex outside marriage, lashing lesbians and slicing limbs off thieves under a disturbing new penal code.

The department’s secret archive on power-crazed Sultan Hassanal Bolkiah stretches back to 1984, when Brunei became independent from British rule.

Prince Charles attended the independence day celebrations, but files about his trip are being kept under lock and key.

The Sandhurst-trained Sultan is a close friend of the British royals, who share a love of polo.

He is also one of the world’s richest men and runs an absolute monarchy, propped up by thousands of British troops permanently stationed in Brunei.

His country is oil-rich and Anglo-Dutch company Shell takes a major share of the profit.

However his half-century in power is now coming under serious international scrutiny, after he introduced gruesome new punishments which he claims will uphold “Islamic” virtues.

The secret Foreign Office files, if they are ever made public, could devastate his family’s claims to religious righteousness.

A dozen documents in the secret archive are understood to detail the Sultan’s trips to Britain, where his family are infamous for hedonistic holidays.

They contain confidential notes about “leading personalities in Brunei” and a “valedictory despatch” by an outgoing British ambassador.

These are the files in which diplomats often make cutting personal remarks about key players in the country where they are stationed.

Another secret file is titled “Brunei: judiciary,” containing details on the institution now tasked with handing out these gruesome punishments.

Other files were transferred to the National Archives in Kew, west London, but kept in a “closed” vault that the public is barred from.

The most secret file, which will remain secret for a century after it was written, contains papers about the “Brunei Royal Family” from 1985.

Other censored files at Kew discuss the Brunei Investment Agency, the Sultan’s business empire which some Hollywood celebrities are now boycotting; papers on Britain’s supply of weapons and troops to Brunei; records referring to dissidents and human rights in the Sultanate.

The Foreign Office declined to comment.