Foreign Secretary Jeremy Hunt has warned there will be "serious diplomatic consequences" if the British academic jailed for life accused of spying in the United Arab Emirates is not freed.
Mr Hunt said the government did not see any evidence for the charges made against Matthew Hedges and that there was concern for his welfare.
Mr Hedges, 31, shook as he was handed his sentence on Wednesday at his third court appearance since his arrest in Dubai Airport on May 5.
His wife Daniela Tejada, who was in court, said: "I am in complete shock and I don't know what to do".
Speaking on Wednesday evening, Mr Hunt said: "We're very concerned for his welfare. UAE is supposed to be a friend and ally of Britain's We've given them repeated assurances about Matthew.
"If we can't resolve this there are going to be serious diplomatic consequences because this is totally unexceptionable.
"We will do everything we can to get him home."
Reiterating the Foreign Office's stance, Prime minister Theresa May said she was "deeply disappointed and concerned" about the case and would be raising it with the Emirati authorities "at the highest level".
Speaking after the hearing, the academic's wife, Ms Tejada, said: "Matthew is innocent. The Foreign Office know this and have made it clear to the UAE authorities that Matthew is not a spy for them.
"This whole case has been handled appallingly from the very beginning with no one taking Matthew's case seriously.
"The British Government must take a stand now for Matthew, one of their citizens.
"They say that the UAE is an ally, but the overwhelmingly arbitrary handling of Matt's case indicates a scarily different reality, for which Matt and I are being made to pay a devastatingly high price.
"This has been the worst six months of my life, let alone for Matt, who was shaking when he heard the verdict. The UAE authorities should feel ashamed for such an obvious injustice."
Mr Hedges, a specialist in Middle Eastern studies at Durham University, went to the UAE to research his PhD thesis, where he was accused of spying for the British Government and arrested.
The Vice-Chancellor of Durham University said the "judgment has been delivered in the absence of anything resembling due process or a fair trial."
Professor Stuart Corbridge added: "There has been no information given on what basis Matt was handed this sentence and no reason to believe that Matt was conducting anything other than legitimate academic research.
"We are committed to doing what we can to get Matt home safely and swiftly and we will offer Daniela and Matt's family our full support during the appeal period and thereafter, at what is an unimaginably difficult time for them."