Rebecca Blake, 30, from Dorking, Surrey, and Conor McRedmond, 28, from Tullamore, Co. Offaly, had spent a year fighting the allegations.
Witnesses said recruitment executive Blake stripped off before straddling McRedmond, who had his jeans pulled down.
The pair denied the accusations and yesterday said they were ‘disappointed’ by the outcome, which will see both deported after serving their sentences.
Blake, who was sacked from her £120,000-a-year post, said: ‘I am devastated by this result and gutted this has been dragging on for a year. I cannot wait to get home and start my life now but I am very scared about going to prison.’
McRedmond has been living in Dubai for four years, said: ‘I am disappointed after coming this far and fighting these allegations for so long. I feel they are making an example of us.’
Blake and McRedmond do not have to go to jail immediately and can decide when to hand themselves in – but if they are arrested in the meantime or get into trouble with the law, they will be taken straight to prison.
They cannot leave the country until they have served their sentence. The pair said they had been financially crippled by the case after spending more than €50,000 fighting to clear their names.
Blake, who moved to Dubai in September 2011, has not been able to find work since she was sacked and neither of them can leave the country after having their passports confiscated.
Blake and McRedmond were arrested on May 4 last year after going on a ten-hour drinking binge. The pair met hours earlier at a brunch, where they admitted getting drunk on free-flowing wine and vodka in an all-inclusive €45-a-head deal.
They carried on drinking at a hotel and got into a taxi together at about 10pm.
Taxi driver Qaiser Khan, 30, claimed within minutes of getting in, Blake had taken her top off and was writhing on top of McRedmond while ‘making the sounds of a woman having sex’.
He pulled over on Sheikh Zayed road and summoned policeman Abdullah Obaid Khamis, who told the court that he found the pair having sex and interrupted them by tapping on the window.
He told prosecutors: ‘They kept having sex for four minutes. The man’s shirt was open, his trousers were down to his knees and the woman was not wearing any underwear.’
The taxi driver alleged Blake offered him ‘a lot of money’ to tell prosecutors they had been kissing rather than having sex, but he refused.
Blake and McRedmond, who works as a manager at Kelly Steel engineering firm, said the allegations had been trumped up after they rowed with the taxi driver about taking a longer route home.
The pair were originally convicted in November in the criminal court, where they were both sentenced to three months in jail and given a €630 fine for drinking alcohol – a crime in the Islamic country.
The sentence was challenged in the Court of Appeal in February, which cut the sentence by a month and reduced the fine.
But the Supreme Court – the highest court in the United Arab Emirates – refused to drop the charges altogether, despite medical reports proving the couple did not made love.
Their lawyer Shaker al Shammary yesterday said the statements of the two witnesses were inconsistent, adding: ‘They threatened to complain about the taxi driver and he beat them to it – yet there is no mention of their dispute in the Supreme Court judgment.
‘The medical records show what the witnesses said was not true but this was not taken into account in the ruling.’
The duo’s only options now are to beg for a royal pardon from Sheikh Mohammed bin Rashid al Maktoum, the ruler of Dubai, or they can serve their time and challenge the deportation order in the courts.
McRedmond said: ‘We find ourselves in exactly the same position we were in after the original verdict but thousands of pounds poorer.
‘Any court in the world would accept the medical evidence above all else. I love Dubai and wanted to carry on living here but I am left without a choice.’
There were fears their failure to clear their names is part of a crackdown from Dubai authorities on expats flouting their strict rules.
Vince Acors and Michelle Palmer, a British couple caught having sex on a beach, were treated more leniently in 2008 when they were convicted on the same charge of indecency and ordered to serve three months in prison, but received a suspended sentence on appeal.