The Post Office has admitted writing to ministers saying it would stand by the prosecution of more than half of the post office operators targeted during the Horizon scandal as recently as last month. Despite the outpouring of concern and anger after what has been described as Britain’s worst miscarriage of justice, the letter from the Post Office’s chief executive, Nick Read, showed it would oppose attempts to overturn the prosecutions in 369 cases. The letter was quietly published by the Post Office as the government confirmed on Thursday it was pressing ahead with its legislation to automatically quash convictions linked to the scandal by July. It showed that Read wrote to Alex Chalk, the justice secretary, to say the Post Office would be “bound to oppose” appeals in 369 cases, less than a week after the ITV drama Mr Bates v the Post Office finished airing. The next day, under public pressure, Rishi Sunak announced a plan for the mass overturning of convictions through an act of parliament. Read’s letter suggests that the Post Office would be legally “bound” to oppose attempts to overturn the convictions. However, former Post Office chair Henry Staunton has claimed the letter was part of an attempt to undermine the government’s mass exoneration plan. Liam Byrne, the Labour MP and chair of the business committee, who will question Read next week, said: “This is further evidence the Post Office is out of control and needs a legally binding instruction to deliver.” In his letter to Chalk dated 9 January, Read wrote that the government’s decisions needed to be “fully informed”. He said that, after an external legal review, the Post Office deemed that it would have opposed appeals from 369 of 700-odd post office operators it prosecuted if they came to court because non-Horizon evidence supported those convictions. Read wrote that in 369 cases the Post Office “would be bound to oppose an appeal”, both because of a court judgment and other information available to the organisation. Read wrote that another 11 cases were still under review, and that in a further 132 cases there was insufficient evidence to take a decision either way. Only 30 further convictions were identified as likely to be wrongful. The Post Office’s letter was copied to Kemi Badenoch, the business secretary, and Kevin Hollinrake, the Post Office minister, on Thursday. It follows a claim made by Staunton, who revealed last weekend that the letter had been sent. According to Staunton, Read sent this letter at the behest of UK Government Investments (UKGI), the body that manages the government’s ownership of the Post Office. UKGI categorically denied this. A spokesperson said: “We strongly refute the claims levelled by Mr Staunton, both in the facts presented and the suggestions made as to UKGI’s overall role. UKGI did not commission the letter as Mr Staunton has claimed and only became aware of it once it had been shared with ministers. It is not UKGI’s role to set [government] policy on these issues which is rightly the role of the relevant departments.” In the letter, Read wrote: “This clearly raises acute political, judicial, and communications challenges against the very significant public and parliamentary pressure for some form of acceleration or by-passing of the normal appeals process. “We make absolutely no value judgment about what you and your colleagues determine as the right course of action, but consider it essential for you to understand the very real and sensitive complexities presented.” Attached to Read’s letter was a legal opinion from the Post Office’s solicitors at Peters & Peters. The firm’s head of business crime, Nick Vamos, wrote that “it is highly likely that the vast majority of people who have not yet appealed were, in fact, guilty as charged and were safely convicted”. On its website, the Post Office said the Peters & Peters note expressed “the personal views of its author” and that “the Post Office was in no way seeking to persuade government against mass exoneration”. Kevan Jones, the Labour MP who has campaigned on the issue since 2009, said it was “remarkable” that the Post Office had written this letter as recently as last month. “I’m asking who instructed Read and on what basis was this letter written,” he said. “The secretary of state said Read did this of his own volition. I find that very difficult to believe having been involved in the advisory board discussions for the last few weeks.” Between 1999 and 2015, the Post Office prosecuted hundreds of post office operators after a faulty IT system, Horizon, made it look like money was missing. There have been more than 900 convictions linked to the scandal – 700 of them brought by the Post Office – with only about 100 overturned so far. It has come to be seen as one of the biggest miscarriages of justice in British history. Read is due to appear before the House of Commons business select committee on Tuesday next week. On Monday Badenoch told MPs: “The only possible answer is that Nick Read himself decided to write that letter. I did not ask him to write it, the Post Office says that it did not, and UKGI did not.” On the webpage where it published the letters, the Post Office said: “Post Office are fully supportive of any steps taken by government to speed up the exoneration of those with wrongful convictions and to provide redress to victims, with the information having been provided to inform that consideration.” In a written ministerial statement, Hollinrake wrote that while “the legislation is likely to exonerate a number of people who were, in fact, guilty of a crime … this is a price worth paying in order to ensure that many innocent people are exonerated”.