Former Post Office boss Paula Vennells will give evidence at the next stage of the inquiry into the Horizon IT scandal.
Ms Vennells, who was chief executive officer of Post Office Ltd between 2012 and 2019, has come under fire over why hundreds of subpostmasters were wrongly prosecuted for fraud and false accounting under her watch.
Glitches in the Horizon IT system used by the Post Office meant money looked as if it was missing from many branch accounts when in fact it was not.
The scandal, which was ongoing from 1999 until 2015, represents one of the biggest miscarriages of justice in UK legal history and more than 100 subpostmasters have had their convictions quashed by the Court of Appeal.
Many more are yet to be cleared and the Government has come under fire for the compensation awarded to victims.
Ms Vennells, who joined the Post Office in 2007, handed back her CBE for services to the Post Office and to charity last month after public anger following the screening of ITV drama Mr Bates vs The Post Office.
After handing it back she told the PA news agency in a statement that she will “support and focus on co-operating with the inquiry”.
She added: “I have so far maintained my silence as I considered it inappropriate to comment publicly while the inquiry remains ongoing and before I have provided my oral evidence.
“I now intend to continue to focus on assisting the inquiry and will not make any further public comment until it has concluded.”
Angela van den Bogerd, former Post Office head of partnerships, Adam Crozier, who was chief executive of Royal Mail from February 2003 to 2010, and Dame Moya Greene, who replaced him and left in 2018, will all give evidence.
Alan Bates will also give evidence to the inquiry when it resumes in April.
Others set to testify in phases five and six include Lord Arbuthnot of Edrom, who campaigned on behalf of subpostmasters when he was Conservative MP for North East Hampshire.
Conservative ministers who will be questioned over their role as the scandal developed include Greg Clark, business secretary from 2016-2019, Kelly Tolhurst, postal services minister from July 2018 to February 2020, Margot James, who held the role between July 2016 and January 2018, and Cabinet Office minister Baroness Neville-Rolfe, who was postal affairs minister in 2015.
Liberal Democrat politicians Sir Vince Cable, the former business secretary, party leader Sir Ed Davey, who was postal affairs minister from May 2010 to February 2012, and Jo Swinson, postal affairs minister from September 2012 to May 2015, will all appear as witnesses.
Labour shadow cabinet member Pat McFadden, who was postal affairs minister from June 2007 to June 2009, will also be questioned.