The former chief executive of Royal Mail, Adam Crozier, and the campaigner Alan Bates will give evidence over the Post Office Horizon scandal this week as the public inquiry into the scandal enters its next phase.

Crozier, who headed Royal Mail when it owned the Post Office between 2003 and 2010, will on Friday provide detailed testimony about his actions for the first time.

Bates, a former post office operator, was played by the actor Toby Jones in the ITV hit drama Mr Bates vs the Post Office, which attracted 14 million viewers and portrayed the victims’ fight for justice. Earlier this year the programme ignited a public furore about the Post Office scandal.

Bates, who appeared before MPs in January, will give evidence to the inquiry on Tuesday.

Now chair of BT, Crozier left Royal Mail in 2010 to run ITV, leaving in 2017. The ITV drama did not feature him and he has so far only issued a short statement, stating his “heartfelt sympathies to the individuals and families who were so wronged by the tragic miscarriages of justice”.

He will be followed in the coming weeks by former directors of the Post Office including Paula Vennells, who will be grilled about why the state-owned body wrongly prosecuted hundreds of people.

Post office operators suffered bankruptcy, prison sentences and homelessness after they were prosecuted for theft and false accounting in what MPs have described as the worst miscarriage of justice in British legal history.

The Post Office hounded operators for more than a decade, alleging that they were to blame for accounting shortfalls in their branch accounts. It has since emerged that the Post Office’s Horizon computer system, which was developed by the Japanese IT company Fujitsu, suffered from IT bugs and its accounting data was unreliable.

In its latest hearings, the inquiry is set to question senior former Post Office and Royal Mail executives under oath, many of whom are speaking for the first time about the scandal.

Alan Cook, the former managing director of Post Office who went on to chair the insurer Liverpool Victoria, will also appear on Friday. Allan Leighton, the ex-chief executive of Asda who was a former chair of Royal Mail between 2002 and 2009, will testify later this month.

Paula Vennells, who was chief executive of the Post Office between 2012 and 2019, will be grilled for three days next month.

The inquiry, chaired by the retired judge Sir Wyn Williams, began in 2022.

In its most recent set of hearings, which ended in February, it emerged that Fujitsu had identified IT bugs in Horizon back in 1999. Fujitsu’s Europe chief, Paul Patterson, told the inquiry that he found it “shameful and appalling” that criminal courts hearing the prosecutions had not been told of the IT problems.

More than 900 post office operators were convicted in the courts using IT evidence from the Horizon computer system, including 700 convictions secured by the Post Office between 1999 and 2015.

103 convictions have been overturned so far and legislation is being introduced by the government to exonerate post office operators prosecuted between September 1996 and December 2018.

Vennells has apologised to post office operators and earlier this year agreed to hand back her CBE after her handling of the Horizon crisis.

A group of MPs is now considering action against her after Channel 4 this month aired audio recordings purporting to show that it was likely that Vennells knew as early as 2013 that the Post Office computer system could be remotely accessed by IT staff. In 2015 Vennells continued to deny to parliament that remote access was possible.

Liam Byrne, Labour MP and chair of the business and trade select committee, said he was considering all options “including the Commons exercising its powers in relation to contempt of parliament” although he did not want to jeopardise future legal action.

The Post Office said of the tapes: “We remain fully focused on getting to the truth of what happened and supporting the statutory public inquiry.”

Vennells said in a statement: “I continue to support and focus on co-operating with the inquiry and expect to be giving evidence in the coming months.

“I am truly sorry for the devastation caused to the sub-postmasters and their families, whose lives were torn apart by being wrongly accused and wrongly prosecuted as a result of the Horizon system.

“I now intend to continue to focus on assisting the inquiry and will not make any further public comment until it has concluded.”

Tim Parker, who chaired the Post Office between 2015 and 2022, will be questioned for two days in July.

Sir Ed Davey, leader of the Liberal Democrats and postal affairs minister between 2010 and 2012, will appear in July along with the Lib Dem former business secretary Sir Vince Cable.