Hundreds of sub-postmasters were prosecuted between 2000 and 2014 after a software glitch in the Post Office's IT system Horizon resulted in shortfalls in accounts.

In December 2019, the Post Office agreed to settle claims made by 555 sub-postmasters, and on Friday, 39 sub-postmasters had their criminal convictions overturned by the Court of Appeal.

Vennells, who was Post Office chief executive between 2012 and 2019, said she was "truly sorry" for the suffering caused to the 39 sub-postmasters as a result of their convictions.

"It is obvious that my involvement with the Post Office has become a distraction from the good work undertaken by the boards I serve," she said in a statement. 

"I have therefore stepped down with immediate effect from all of my board positions, and intend to focus fully on working with the ongoing government inquiry to ensure the affected sub-postmasters and wider public get the answers they deserve."

She had held non-executive director roles at Morrisons since 2016 and at Dunelm since 2019.

Vennells on Sunday said she would also step back from her duties as an ordained Church of England minister.

(Reporting by Paul Sandle; editing by James Davey)