The 49-year-old was jailed last year on controversial terrorism charges, but was allowed to travel to Britain in January for spinal cord surgery after he fell ill in prison.
Nasheed claimed today he had "no choice" but to work from exile against President Abdulla Yameen.
"Former Maldives president Mohamed Nasheed has refugee status in the UK," a statement on his website said.
Nasheed became the first democratically-elected president of the Indian Ocean island nation in 2008 and served for four years before he was toppled in what he called a coup backed by the military and police.
More From This Section
"President Yameen has jailed every opposition leader and cracked down on anyone who dares to oppose or criticise him," Nasheed said in the statement proclaiming his refugee status.
"In the past year, freedom of the press, expression and assembly have all been lost.
"Given the slide towards authoritarianism in the Maldives, myself and other opposition politicians feel we have no choice but to work from exile -- for now."
Britain's Home Office interior ministry declined to comment when contacted by AFP.
The Maldives has suffered prolonged political unrest in recent years, seriously denting its reputation as an upmarket tourist destination.
Yameen is a half-brother of Maumoon Abdul Gayoom, who ruled for 30 years until his defeat by Nasheed in the country's first multi-party elections eight years ago.
Western countries and the United Nations have widely criticised Nasheed's trial and jailing.
He was accorded a red carpet welcome and received by Prime Minister David Cameron after arriving in Britain in January in a deal brokered by the former colonial power along with Sri Lanka and India.