The scandal led to the convictions of hundreds of sub-postmasters.

The Horizon issue has come to public attention following the airing of ITV drama Mr Bates vs The Post Office which returned the spotlight to the scandal.

Between 1999 and 2015, more than 700 Post Office branch managers were convicted after the faulty Horizon software made it look like money was missing from their shops.

Ms 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.

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"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 am, however, aware of the calls from sub-postmasters and others to return my CBE.

"I have listened and I confirm that I return my CBE with immediate effect.

"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."

A government source told Sky News that Ms Vennells handing back the honour was "the right thing to do".

Labour's Kevan Jones told Sky News he was "bemused" by the government's response, as it nominated Ms Vennells for the honour in 2019.

Lord Arbuthnot, a former Conservative MP who campaigned on the Horizon scandal, told Sky News that if he had been in Ms Vennells's position he would not have taken the honour in the first place.

He said: "There were many people who behaved really badly, among them, Paula Vennells, of course.

"But I'm pleased that this has now happened because it means that the subpostmasters can begin to concentrate on the wider picture."

Who is Paula Vennells?

While honours can only be forfeited to the King, a recipient can renounce theirs voluntarily.

This involves them ceasing to refer to themselves with the title while they go through the process to get it annulled by the monarch.

Ms Vennells joined the Post Office as group network director in 2007, having previously worked at Unilever, L'Oreal, Dixons, Argos and Whitbread.

She is also an ordained priest.

Ms Vennells was made chief executive of the Post Office in 2012, the year the company split from Royal Mail.

The Post Office had been prosecuting sub-postmasters and sub-postmistresses since 2000. It was the year Ms Vennells took over that the company began investigating allegations about the Horizon system.

Five years later, in 2017, a group of staff managed to bring a case against the Post Office in the High Court.

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What is the Post Office scandal

Ms Vennells came under increasing criticism, and eventually stepped down in 2019, when she received her CBE.

When a judge said in 2019 that sub-postmasters and sub-postmistresses should have their convictions overturned, Ms Vennells said she was "truly sorry for the suffering caused".

Ms Vennells is not the only person or entity to have faced criticism for her actions during the scandal.

Sir Ed Davey, who was postal minister during the coalition years, has had to fend off calls to resign. He said on Monday that the Post Office spun a "conspiracy of lies".

The prime minister's spokesman said that Fujitsu would be "held to account, whether legally or financially" if it is found to to be responsibly for the scandal. Fujitsu developed the Horizon software which was at fault.

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A Fujitsu spokesperson said: "The current Post Office Horizon IT statutory inquiry is examining complex events stretching back over 20 years to understand who knew what, when, and what they did with that knowledge.

"The inquiry has reinforced the devastating impact on postmasters' lives and that of their families, and Fujitsu has apologised for its role in their suffering.

"Fujitsu is fully committed to supporting the Inquiry in order to understand what happened and to learn from it. Out of respect for the inquiry process, it would be inappropriate for Fujitsu to comment further at this time."