Yingluck, 50, was due on Friday morning to arrive at the Supreme Court for the ruling in her trial for criminal negligence that could have seen her jailed for 10 years.
But she did not show up, wrong-footing the court and her supporters alike as she wrote a dramatic closing chapter to the 16-year political saga of her mega-rich Shinawatra family.
The junta source, who is well-placed in the security hierarchy, gave a detailed description of her escape, saying she took a private jet from Thailand to Singapore and onto Dubai, the base of Shinawatra family patriarch Thaksin, who is Yingluck's older brother.
"Thaksin has long prepared escape plan for his sister... he would not allow his sister to spend even a single day in prison," the source told AFP, requesting anonymity.
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"But Dubai is not Yingluck's final destination," the source said, adding she may be aiming "to claim asylum in Britain".
The Shinawatra's political network remained tight-lipped today in a media blackout that only served to heighten speculation over her dash from Thailand and the likelihood of a possible deal with the junta to allow her to leave.
A senior source inside the family's Pheu Thai party, also requesting anonymity, on Saturday told AFP Yingluck had fled the country for Dubai a few days before the ruling.
The Shinawatra political dynasty emerged in 2001 with a series of groundbreaking pro-poor welfare schemes that won them elections but rattled Thailand's royalist, army-aligned elite, who battered successive governments linked to the clan with coups, court cases and protests.
Thaksin, Yingluck's elder brother, has been based partly in Dubai since he fled Thailand in 2008 to avoid jail for a corruption conviction. He was toppled from power by a 2006 coup.
Thai newspapers reported that Yingluck fled through a land border to Cambodia, flew to Singapore and on to Dubai, perhaps two days before her court date.
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