An 18-year-old man from London has been sentenced to one year in a Dubai jail for having a sexual relationship with a 17-year-old girl, a campaign group has said.

Marcus Fakana, of Tottenham, north London, “feels abandoned by the British government and Keir Starmer”, said Detained in Dubai.

Radha Stirling, the group’s chief executive, said the sentence was an “utter disgrace” and “an embarrassment to Britain”, and claimed: “The UK has prioritised trade deals over people’s lives.”

Fakana was with his parents in the United Arab Emirates from the end of August when a “holiday romance blossomed” with another Londoner, who has since turned 18, the campaign group previously said.

After returning to the UK and seeing pictures and chats, the girl’s mother reported the relationship to Dubai police, who then arrested Fakana at his hotel, it is alleged.

A Foreign, Commonwealth and Development Office spokesperson said: “We are supporting a British man in the UAE and are in contact with his family.”

Fakana was held at the notorious al-Barsha police station for three days, unable to make a phone call or speak with his parents, according to Detained in Dubai.

In a statement posted on social media, Stirling said: “The UK was once the most diplomatically influential western country in the Middle East. Now, we are seeing countries like Canada, Malaysia, Ireland and the US leaving the UK way behind.

“The Labour government should be ashamed they have not secured the freedom of a teenage tourist. It wasn’t a difficult job.”

Stirling said Fakana, who has been held in Dubai since September, would appeal against his sentence and was “desperately hoping to come home this week”.

In Dubai, if an adult has a sexual relationship with a person under 18 they can be prosecuted for having a sexual relationship with a minor.

The family have issued a plea to the ruler of Dubai, Sheikh Mohammed bin Rashid al-Maktoum, to spare Fakana.

Stirling said: “I urge young people and parents to reconsider holidays in Dubai where so many people find themselves at risk of unfair and lengthy detention in prisons notorious for human rights abuses and torture. Holidaymakers should book elsewhere until Marcus is free.”

Last month, Fakana told Detained in Dubai that he and the girl “had a wonderful time together” and “really liked each other”, and that he felt frightened when police officers arrested him.

He said he was living in Airbnb accommodation that was costing his family £2,000 a month. Fakana also told the group that Dubai had demanded 10,000 AED (£2,200) for bail.

The teenager has received backing from members of the public, with a Change.org petition calling on the government to offer him stronger support receiving more than 40,000 signatures.

A fundraiser set up by Fakana’s family, “Help bring Marcus home”, has raised more than £35,000, according to GoFundMe.