The letter of request, dated July 5, 2018, cited the treaty between the United Kingdom and Siam on the extradition of fugitive criminals, signed in Bangkok on March 4, 1911.

The letter said Ms Yingluck is a person wanted by Thai authorities to serve a five-year jail term handed down on her by the Supreme Court’s Criminal Division for Persons Holding Political Positions which found her guilty of violating Section 157 of the Criminal Code and Section 123/1 of the Corruption Prevention and Suppression Act of B.E. 2442 (1999).

A warrant has been issued for her arrest since Sept 27, 2017, when the court issued its ruling, the letter said.

Busadee Santipitaks, the Foreign Ministry spokesperson, when asked about this matter, said a Thai official unit is working on an extradition request.

When asked if an official request has been sent to the British government, Ms Busadee said it was “inconvenient” for her to reply now as she was busy helping Thai people affected by an earthquake in Indonesia’s Lombok.

The BBC website said the Foreign and Common Weath Office of the British government also declined to comment on this matter and referred it to the Home Office.

The Home Office of the British government replied in an e-mail that it has been its policy and line of practice not to confirm or deny whether the office has received a request for an extradition of a person until that person has been arrested.