It was not immediately clear why the government had waited until now to seek Yingluck's extradition or how Britain would respond
Thailand has asked Britain to extradite former prime minister Yingluck Shinawatra, overthrown in a coup in 2014 and sentenced in absentia to jail for negligence, Prime Minister Prayuth Chan-ocha said on Tuesday.
Yingluck fled the country last August to avoid being jailed over a rice subsidy scheme that ran up losses in the billions of dollars. She has denied wrongdoing and said the trial was politically motivated.
The Supreme Court sentenced her in absentia to five years' jail last September.
Prayuth said the request was a necessary procedure between the two countries which share an extradition treaty.
"We cannot go and arrest people abroad so it is up to that country to arrest and send (her) to us," Prayuth said.
Yingluck and her brother, ousted former prime minister Thaksin Shinawatra, have been at the centre of a power struggle that has dominated Thai politics for more than a decade, pitting traditional royalist and the military elite against the Shinawatra family and their supporters in the rural north and northeast.
It was not immediately clear why the government had waited until now to seek Yingluck's extradition or how Britain would respond.
With a long-awaited general election due for some time next year, both Thaksin and Yingluck still wield significant political influence.
The junta has long maintained that it is unconcerned by the Shinawatra siblings but critics say the military is looking to end the family's political influence by introducing a new military-backed constitution and restrictions on political parties.