British Prime Minister David Cameron pledged on Saturday to apply pressure on the Maldives to improve the rule of law and free political prisoners after meeting the country's former president after his temporary release from jail.

Mohamed Nasheed, the Maldives' first democratically elected president, is serving a 13-year sentence on terrorism charges for the alleged abduction of a judge after a rapid trial last March which drew international criticism.

Nasheed and his lawyer Amal Clooney met Cameron at Downing Street in London on Saturday after the former president gained permission to travel to Britain for surgery. The Maldives gained independence from the United Kingdom in the 1960s.

"Following his release from prison, Mr Nasheed thanked the Prime Minister for the role the UK had played by continuing to raise his case, including with other countries," a statement from Cameron's office said.

Downing Street said the two men had agreed that a Commonwealth meeting to be held in the Maldives next month would provide an opportunity to press the Maldivian government to engage in "open political dialogue and free all remaining political prisoners swiftly".

"The Prime Minister told Mr Nasheed that the UK would continue to raise concerns about the erosion of democracy and wider situation in the Maldives and it would also continue to discuss the situation with international partners," it said.

Nasheed was ousted in disputed circumstances in 2012 for ordering the arrest of a judge. The United Nations, the United States and human rights groups have said President Abdullah Yameen's government failed to follow due process and that the case was politically motivated.