Brunei has defended its draconian anti-homosexual and anti-adultery laws in a letter to the European Parliament (EP), while saying that few homosexuals are stoned to death in practice.

The south-east Asian country of 400,000 recently passed laws where homosexuals and others who commit adultery face brutal executions through a penal sentence known as "hadd".

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The architect behind the sharia laws, the 72-year old sultan Hassanal Bolkiah, who has ruled the oil-rich nation for decades, has since turned into an international pariah amid celebrity boycotts of his luxury hotels.

But the Brunei mission to the EU defended its position in a letter to MEPs ahead of a debate on human rights in the EP in Strasbourg on Thursday (18 April).

The criminalisation of adultery and sodomy were needed to safeguard the sanctity of family lineages and marriage, its four-page memo, obtained by EUoserver said.

The criminal offences did not apply to non-Muslims, it added.

And the harshest of the punishments, such as stoning to death of gay men, were seldom carried out because there were too few robust witnesses to fulfil legal requirements, it also said.

At least two males of "high moral standing piety" must witness the crime of sodomy or adultery, it noted.

But the difficulty in finding such men meant the stonings were unlikely to occur in practice, the Brunei diplomats added.

"The standards of piety of the male witness is extremely high, [so] that it is extremely difficult to find one in this day and age," their letter said.

The Brunei embassy further noted that its anti-gay sharia law was meant to prevent the alleged crimes from taking place instead of punishing people after the fact.

Meanwhile, people who committed less severe "crimes" were to be whipped by people of the same gender, it said.

Only moderate force was to be used and the whipping should not result in the "laceration of the skin" or "break bones", it added.

The European Union has said any such punishments violate the Convention against Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment.

Brunei signed the convention in 2015.