Senator Somchai Sawangkarn has confirmed that jailed former prime minister Thaksin Shinawatra will be eligible for early release in February after completing half of his one-year jail term.

Mr Somchai said Thaksin can still receive a reduction in jail time even though his eight-year term has already been commuted to one year.

Shortly after his return from self-imposed exile, Thaksin petitioned His Majesty the King for a royal pardon and got his sentence shortened.

Citing the Department of Corrections, Mr Somchai said inmates must serve one-third of their sentences to be eligible for a reduction on special occasions. In Thaksin's case, he will have completed one-third of his prison term by Dec 20 and half of it in February.

He said Thaksin will be eligible for a suspended jail term after six months because he is an elderly inmate with chronic diseases, and he would not need to wear a tracking device.

"In case of an early release, an electronic monitoring (EM) ankle bracelet is unnecessary. He may be confined to his house and would not be allowed to travel overseas. The six-month period [before he is eligible for early release] includes his stay in hospital," he said.

Thaksin, 74, was admitted to Police General Hospital on the night of Aug 22, about 13 hours after he was sent to prison. He has now been there for over a month, prompting questions over privileged treatment.

Mr Somchai said his Senate committee urged the Royal Thai Police and Police General Hospital to at least inform the public how long Thaksin is expected to stay there before he can be sent back to the Corrections Hospital.