Four former lawmakers were on Tuesday released from prison after completing their jail terms for conspiracy to subversion in the city's largest national security trial to date.

Gary Fan, Claudia Mo, Jeremy Tam and Kwok Ka-ki had each served four years and two months behind bars.

Vehicles believed to be carrying the former legislators were seen leaving Shek Pik Prison, Lo Wu Correctional Institution and Stanley Prison where they had served time.

Mo's husband confirmed that she has returned home to rest and it was not suitable for her to give media interviews.

The four were among 45 people sentenced in November last year for their involvement in an unsanctioned Legislative Council primary poll in a plot to overthrow the government.