The Sultan of Brunei, an absolute monarch who pays for a garrison of British troops to be stationed is his oil rich nation, will on Thursday dismiss the concerns of human rights campaigners and start imposing sharia law. Many of the laws, which include the dismemberment of limbs and stoning to death, will apply to both Muslims and non-Muslims.

Sultan Hassanal Bolkiahhe, 67, announced last year that he wanted to introduce a full sharia system and warned critics who took to social media that they could be prosecuted. “It is because of our need that Allah the Almighty, in all his generosity, has created laws for us, so that we can utilise them to obtain justice,” he said at the time.

The decision sparked condemnation from activists, and the leaders of other religions in Brunei expressed concern that they could suffer. The spokesman for the UN high commissioner for human rights said he was “deeply concerned” about the move.

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But the thrice-married sultan has ignored such concerns and pressed ahead with his plans. In speech on Wednesday, he said the first part of a three-phase plan to introduce Islamic law would begin on Thursday.

“Today I place my faith in, and am grateful to Allah the almighty, to announce that tomorrow, Thursday, 1 May, 2014, will see the enforcement of sharia law phase one, to be followed by the other phases,” he said, according to the AFP news agency.

Brunei is two thirds Muslim and has long implemented some sharia, mainly for civil matters such as marriage. But last year the sultan, who is said to be worth £24 billion and lives in a 1,788-room palace, said he wanted to introduce full sharia to guard against the “challenges” of globalisation, including the impact of the Internet.

“When rulers do this, it is usually for domestic political reasons,” said Dr Anicée Van Engeland, a lecturer in law at SOAS, University of London.

Among the offences included in the laws are insulting the Prophet Mohamed, drinking alcohol, getting pregnant outside of marriage and “sodomy”. The latter will be punishable by stoning.

Britain granted independence to Brunei in 1984 but has maintained a close relationship ever since. A 1,000-strong regiment of the British Army, the Royal Gurkha Rifles, has been located there since the late 1950s and is paid for by the sultan. Last year Britain said the British Garrison Brunei, the last British troops stationed in the Far East, was the “linchpin” of relations between the two countries.

In March, the Ministry of Defence said it was in discussion with the authorities in Brunei to clarify whether the new laws would have any impact on the British troops. On Wednesday an MoD spokeswomen she was unable to comment on the outcome of the talks.

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In a statement, Britain’s Shadow Defence Secretary, Vernon Coaker, said it was essential the government explained what discussions had taken place with the sultan.

“We must have clarity about any impact the introduction of sharia law might have on UK forces and their continuing presence in Brunei,” he said.

A spokesman for the Foreign Office said: “We are concerned about Brunei’s decision to introduce a sharia criminal code. Ministers have raised questions about the law’s implications and pressed for a lenient approach.”

Royal Dutch Shell, an Anglo-Dutch multinational, runs two major operations in Brunei as a joint venture with the Brunei government. A spokesman, Jonathan French, said the company would not comment on the possible impact on its employees.

The decision to impose sharia has been met with widespread condemnation. A number of celebrities, including Stephen Fry, urged people to boycott the Dorchester Collection chain of hotels owned by the sultan – among them the Dorchester Hotel in London – because the new law will make homosexuality punishable by death.

On Wednesday, Amnesty International said Brunei’s new laws will introduce stoning to death for acts that should not even be considered crimes. “[The new laws] will take the country back to the dark ages,” said Amnesty’s Rupert Abbott.

While Brunei, which has a total population of 400,000, has sizeable Christian and Buddhist communities. There are an estimated 30,000 Filipino citizens in Brunei, many of them Catholic, and the Philippine embassy has held meetings to explain to its citizens the implications of the new laws. Christian leaders have expressed concern that even baptisms could be in breach of the regulations.

The authorities in Brunei and the Brunei High Commission have repeatedly failed to respond to queries. However, according to a report in the Brunei Times earlier this year, Brunei’s most senior Muslim cleric, Dr Ustaz Hj Awg Abdul Aziz Juned, claimed that those criticising the new rules did not understand them.

The sultan was for many years was involved in a high-profile legal battle with his brother, a playboy accused of misappropriating £9 billion of government assets and who reportedly owned a yacht called Tits.