The jailed Maldivian opposition leader Mohamed Nasheed had his permission to travel abroad for surgery scuttled at the last minute as the authorities demanded a “hostage” in his place, his party said.

“The government backtracks on their decision to unconditionally allow (former) president Nasheed to travel to UK for surgery,” a Maldivian Democratic party spokesman, Hamid Abdul Ghafoor, said on Sunday.

He said the government had insisted on the nomination of a family member to act as a guarantee for his return, after 30 days of treatment in Britain, to serve his 13-year jail term. The guarantor would be a hostage who could be prosecuted if Nasheed did not return, he said.

“It is an ethical issue. That is why President Nasheed has not agreed to the demand of a guarantor,” he added.

The sudden development came hours after the country’s prisons chief, Mohamed Husham, announced that Nasheed had been granted 30 days leave from prison for spinal cord surgery and was expected to leave later Sunday.

“We are making arrangements so that he can travel later today,” Husham had told reporters earlier in the day.

Media reports have said the Maldives government reluctantly softened its stand on Nasheed following diplomatic pressure from neighbouring India and Sri Lanka as well as the former colonial power Britain.

The 48-year-old former president was sentenced on terrorism charges relating to the arrest of an allegedly corrupt judge in 2012, when he was still in power. The UN said his trial was seriously flawed and he should be released and compensated for wrongful detention.

Hardliner Abdulla Yameen, the current president, has refused to accept the UN ruling and is resisting international pressure to release Nasheed.

Britain’s deputy foreign minister Hugo Swire arrived in Malé on Sunday and held talks with Yameen but details were not disclosed.

Nasheed was toppled in February 2012 in what he called a coup, backed by the military and police.