Dubai police said today they had found no evidence to support a British woman's report that she was raped by a waiter in the Gulf Arab emirate, but have arrested her and her boyfriend for having sex outside marriage.

The case is the second time in a just over a year in which Britons have hit the headlines by falling foul of laws banning extra-marital sex in Dubai, a Muslim emirate popular with sun-seeking Western tourists and expatriates.

The woman, 23, and her British boyfriend, 44, were in Dubai as tourists when they reported to police that she had been raped by a Syrian waiter in the bathroom of a hotel bar, Khamis al-Muzinah, deputy commander of the Dubai police, told Reuters.

"The police didn't find any proof that anything happened in the bathroom," Muzinah said.

The investigation found that the British woman had been very drunk and an Indian bartender had helped her find the toilets, where two female staff were present at the time, Muzinah said.

She vomited several times and fell asleep on a chair before being escorted back to her boyfriend by one of the two female staff, he said.

During questioning the following day, the woman told police that she had been sharing a hotel room with her boyfriend and that they had had sex, which led to the couple being arrested.

"They have been charged for having sex without marriage," Muzinah said, adding that the police had now handed the case to the public prosecutor, who would decide whether to bring a court case against them. The couple are currently free, he said.

There was no immediate comment from the couple.

Dubai's foreign population has expanded rapidly in recent years as expatriates flocked to the Gulf Arab trade and tourism hub for its tax-free earnings and year-round sunshine.

The changes have challenged the Emirati population, which is now vastly outnumbered by foreigners, raising concern that their emirate's rapid pace of growth is a threat to their social and religious identity in what remains a deeply conservative region.

In a high-profile case in 2008, a British couple narrowly escaped jail after a Dubai court found them guilty of engaging in drunken sexual activity outside of wedlock, and for doing so in public on a beach in the emirate.

They were sentenced to three months in prison followed by deportation, but had their jail terms overturned on appeal.

The website of the British embassy in Dubai warns Britons of the possible consequences of having sex outside of wedlock.

"Sexual relationships outside of marriage are illegal in Dubai and can attract imprisonment," a list of dos and don'ts in the United Arab Emirates says.

"We can confirm the arrests of two British nationals in Dubai on January 1. The embassy in Dubai is providing consular assistance," Simon Goldsmith, a spokesman for the British embassy, told Reuters.

Muzinah said media reports that the British couple were being treated especially harshly because they are Muslims were incorrect but that marriage may help their situation.

"Muslim or not Muslim -- we will make the case. The mistake is the same for anyone, we have a law against that," he said.

"If they get married the court might stop the case."