A photograph appearing to show Yingluck Shinawatra shopping in London, believed to be the first public sighting of the former premier since she fled the country in August, has officials on the alert once more.

The National Council for Peace and Order (NCPO) is investigating whether the woman in the picture really is Yingluck after the image surfaced on social media yesterday.

First shown by new18 (NewTV), a digital TV news channel, the picture was said to have been taken on Tuesday at Westfield Shopping Centre, Shepherd's Bush, the largest mall in London.

Yingluck appeared to be alone at the time the picture was taken, the channel said.

NCPO spokesman Piyapong Klinpan said security and other agencies were looking into the matter.

A source close to Yingluck said the woman in the photo was "likely" to be the former prime minister but she could not say when it was taken.

“I've visited her in England once [since August] and she was well and in good spirits. It's like she has let go of things, politically," the source said.

Yingluck is leading a "normal" life rather than acting like someone who is on the run but she still avoids places where Thai people may recognise her, the source added.

“She doesn’t go out wearing a disguise but she sometimes wears sunglasses."

Foreign Ministry spokesperson Busadee Santipitaks said the ministry had no information on the matter.

Yingluck, 50, fled Thailand via Cambodia in late August, two days before the scheduled ruling in her negligence case before the Supreme Court’s Criminal Division for Holders of Political Positions.

Thaksin, meanwhile, is said to be spending the New Year holiday in Japan, INN News reported on Friday.

The former premier's daughter Paethongtarn posted a live video stream of her father with his children and grandchildren on her Ing Shinawatra Facebook page.

He was shown cooking beef curry in Niseko, a town on the northern island of Hokkaido.

Thaksin is also a fugitive from justice after he was convicted in absentia in 2008 over a corrupt land deal.