Thailand's Supreme Court convicted Yingluck on Wednesday of dereliction of duty over a controversial rice subsidy program and sentenced her to five years in prison
. The scheme cost the country billions of dollars.
Having already fled the country, Yingluck was not present for the verdict and sentencing.
Yingluck -- ousted by a military coup in 2014 -- had been barred from leaving Thailand without court approval since 2015, when her trial started.
Her bail of 30 million baht ($900,000), posted when the trial began more than two years ago, has been confiscated.
Prime Minister Prayut Chan-o-cha said on Thursday that Yingluck was in hiding in Dubai
, where her brother Thaksin Shinawatra, another former Thai prime minister, lives in exile. But the PTP source told CNN that Yingluck left Dubai for London two weeks ago.
The UK's Home Office, which deals with asylum applications, told CNN it does not comment on individual cases.
Yingluck in 2016: 'I've never thought of fleeing'
In 2016, Yingluck pledged to see through her trial, and said that she had not considered leaving the country.
"I stand firm to fight my case. All eyes are on me. I have duties and responsibilities to carry on.
"I assure you, I've never thought of fleeing," she said.
The rice subsidy program, introduced in 2011, pledged to pay farmers well above the market rate for their crop. But critics said it wasted large amounts of public funds trying to please rural voters -- hurting exports and leaving the government with huge stockpiles of rice it couldn't sell without losing money.
Yingluck said the rice subsidy scheme was "beneficial for the farmers and the country" and that claims it lost money were wrong and motivated by political bias against her.
Yingluck's no-show when the verdict hearing opened in August was a "big surprise" to most people in Thailand, Thitinan Pongsudhirak, a political scientist at Chulalongkorn University told CNN at the time.
"The way that she had fought, it had looked like she was willing to go through with (the trial).
Thitinan said Yingluck's decision to skip the verdict hearing will have "emboldened" the military government.
"They would not have wanted to put her in jail, in this scenario, (but her not showing up for the hearing) puts her on the back foot and gives them an edge."
There was only "low risk" of unrest following her absence, he added.
"The military government have been suppressing dissent and suppressing demonstrations. (Her supporters are) fanned out over the country so it is hard for them to mobilize."
Fall from power
When she was inaugurated in 2011, Yingluck became Thailand's first female prime minister and its youngest in over 60 years.
After the 2014 coup, she was impeached by Thailand's military-appointed National Legislative Assembly. The ruling barred her from political office for five years.
At the time, Yingluck said she had behaved with integrity and honesty during her time as prime minister.
Yingluck was investigated by Thailand's National Anti-Corruption Commission (NACC) amid an outcry over the rice subsidy scandal, and put on trial. Proceedings have lasted more than two years.
Thaksin Shinawatra, Yingluck's brother, was overthrown as Prime Minister in a military coup in 2006. Thaksin is living in self-imposed exile to avoid corruption charges.