The boss of the Post Office wrote a letter to ministers saying he would stand by the prosecution of more than 350 of the sub-postmasters convicted in the Horizon scandal.

Chief executive Nick Read sent the letter to Justice Secretary Alex Chalk last month, informing him that the Post Office would be “bound to oppose” appeals against at least 369 prosecutions.

The document was dated 9 January – the day before the government announced plans for a new law to exonerate and compensate sub-postmasters who had been wrongly convicted in the Horizon scandal.

Mr Read’s letter was published by the Post Office on Thursday, as the government confirmed it was pressing ahead with the legislation to automatically quash convictions by July.

In response, the government said it would introduce “safeguards” to avoid “anyone who was rightly convicted” attempting to “take advantage” of the compensation scheme.

“Innocent post-masters have suffered an intolerable and unprecedented miscarriage of justice at the hands of the Post Office, which is why we are introducing legislation to swiftly exonerate all those convicted as a result of the Horizon scandal,” a government spokesperson said.

In the letter, Mr Read wrote that the Post Office had conducted an external legal review into prosecutions linked to the Horizon IT system between 1999 and 2015.

The period saw hundreds of sub-postmasters prosecuted because of discrepancies in the IT system, in what has been called the biggest miscarriage of justice in UK history.

Mr Read wrote that the review found that the Post Office was “bound” to oppose appeals against 369 of the roughly 700 prosecutions made in the period of the Horizon scandal because the evidence relied on in these cases was unrelated to the faulty system.

He wrote that a further 11 cases were under review, while there was insufficient evidence to take a decision either way in 132 cases.

“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,” he wrote.

Attached to Mr Read’s letter was a note by Nick Vamos, the head of business crime at Peters & Peters, the solicitors for the Post Office.

In the note, Mr Vamos wrote that it was “highly likely that the vast majority of people who have not yet appealed were, in fact, guilty as charged and were safely convicted”.

The publication of the letters comes after allegations from the former chairman of the Post Office, Henry Staunton, who claimed there was “no real movement” on payouts to sub-postmasters until after the airing of ITV drama Mr Bates Vs The Post Office earlier this year.

Read more from Sky News:
Post Office Horizon scandal: The unanswered questions about legislation
Who is former Post Office chairman, Henry Staunton?

The claim was denied by the government and sparked a high-profile row between Mr Staunton and Business Secretary Kemi Badenoch.

While making the allegations, Mr Staunton revealed the existence of Mr Read’s letter.

The Post Office published the letter and the note on Thursday with a comment which said they were sent to “explain the work that the Post Office had requested its legal counsel, Peters & Peters, undertake to proactively identify, on the papers available, any convictions that could be unsafe”.

“This was primarily to offer the government any support that might assist them as they consider relevant issues in advance of passing legislation, without any value judgement on what the correct course of action might be,” it said in a statement, alongside publishing the letters.

The Post Office also said the note provided by Peters & Peters was “not solicited” by them and was sent to “express the personal views of its author”.

“(The) Post Office was in no way seeking to persuade the government against mass exoneration,” it said.

“We 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.”

On Thursday, the government announced it aimed to get the exonerations done “as soon as possible before the summer recess” on 23 July.

Writing to the House of Commons, Post Office minister Kevin Hollinrake said: “As noted in my statement on 10 January, the legislation is likely to exonerate a number of people who were, in fact, guilty of a crime.

“The government accepts that this is a price worth paying in order to ensure that many innocent people are exonerated.”

In an attempt to ensure people are truthful in signing up for compensation linked to convictions being overturned, they will have to sign a disclaimer confirming their innocence.

“Any person found to have signed such a statement falsely in order to gain compensation may be guilty of fraud,” Mr Hollinrake added.

An independent public statutory inquiry is ongoing to establish a clear account of the implementation and failings of the Horizon IT system at the Post Office over its lifetime.