Two former north Norfolk sub-postmistresses are among 39 who have just had their convictions quashed after what has been called "the UK's most widespread miscarriage of justice".

Alison Henderson and Siobhan Sayer were among the former postmasters and mistresses who were convicted of stealing money after the Post Office's installation of a faulty computer system called Horizon in 1999.

Ms Sayer, who worked at Erpingham Post Office, was given a suspended jail sentence at Norwich Crown Court in 2010 after she was falsely convicted of defrauding Royal Mail out of nearly £19,000.

Ms Henderson, who worked at Worstead Post Office, was also falsely convicted at Norwich Crown Court in 2010. It was said she had covered up her losses of nearly £12,000 by false accounting.

In a statement after the ruling at the Royal Courts of Justice in London, Post Office chairman Tim Parker said: “The Post Office is extremely sorry for the impact on the lives of these postmasters and their families that was caused by historical failures.

“Post Office stopped prosecutions soon after its separation from Royal Mail a decade ago and has throughout this appeals process supported the overturning of the vast majority of convictions.

“We are contacting other postmasters and Post Office workers with criminal convictions from past private Post Office prosecutions that may be affected, to assist them to appeal should they wish.

“Post Office continues to reform its operations and culture to ensure such events can never happen again.”

The Court of Appeal also allowed 39 of the appeals on the basis that their prosecutions were an affront to the public conscience.

Lord Justice Holroyde, sitting with Mr Justice Picken and Mrs Justice Farbey, said: “Post Office Limited’s failures of investigation and disclosure were so egregious as to make the prosecution of any of the ‘Horizon cases’ an affront to the conscience of the court.”

However, three of the former subpostmasters – Wendy Cousins, Stanley Fell and Neelam Hussain – had their appeals dismissed by the court.

Lord Justice Holroyde said the Court of Appeal had concluded that, in those three cases, “the reliability of Horizon data was not essential to the prosecution case and that the convictions are safe”.