Mr Bates was also described as "unmanageable" by a former managing director at the organisation, documents disclosed at the inquiry into the Horizon IT scandal have revealed.

Appearing before the inquiry today, Mr Bates said the Post Office "didn't like me standing up to them" - and argued that they terminated his contract as a result.

His answers were said to be sobering and compelling by current Post Office chief executive Nick Read, who was speaking to reporters outside the inquiry.

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Mr Bates's role in bringing the scandal to light reached new levels of awareness in early January, when he was portrayed by actor Toby Jones in the ITV drama Mr Bates Vs The Post Office.

Public and political interest in the industrial-scale miscarriage of justice suffered by sub-postmasters was transformed by the television drama.

Hundreds of sub-postmasters were prosecuted for theft and false accounting, while many more were ostracised and forced to leave their communities having borrowed large sums or lost their homes in an attempt to make up losses, many of which turned out to be due to errors in the Horizon accounting software used by the Post Office.

When asked in the afternoon for his thoughts on the culture of the Post Office, he described it as an "atrocious organisation", adding that it was "beyond saving".

"They need disbanding, it needs removing," he said.

"It needs building up again from the ground floor.

"The whole of the postal service nowadays - it's a dead duck. It's beyond saving.

"It needs to be sold to someone like Amazon.

"It needs a real big injection of money and I only think that can happen coming in from the outside," he added, "otherwise it's going to be a bugbear for the government for years to come".

What the Post Office knew in the early 2000s

The inquiry heard today that Mr Bates was in regular contact with the Post Office's IT helpdesk and in the early 2000s wrote to officials in the organisation detailing his numerous problems with the Horizon system.

Over two years and nine months, while Mr Bates and his assistants were running his Post Office branch in Llandudno, Wales, they made 507 calls to the helpline - of which 85 related to Horizon and balancing problems.

A loss generated by Mr Bates's branch was formally written off at the Post Office via a standard form with a "delete as appropriate" box.

At the time Mr Bates recalled hearing a manager at the Post Office say: "Oh, it's another one - the Horizon losses."

It wasn't until 2015 that the Post Office ceased prosecuting sub-postmasters using wrongful data from Horizon.

No apology was made until 2019 after a successful High Court challenge taken by Mr Bates and other sub-postmaster victims.

How Post Office dealt with Mr Bates

After persistently flagging issues to officials and refusing to repay a loss generated by Horizon, Mr Bates was dismissed, by letter, with no reason given for the firing.

A Post Office manager had instructed Mr Bates to make good the loss of roughly £1,000 shown in his accounting by the IT system.

Asked what he understood to be the reason for the termination, Mr Bates said: "Basically, I think it was because a) they didn't like me standing up to them in the first instance; b) they were finding it awkward; and c) I don't think they could answer these questions and they had a feeling I was going to carry on in a similar vein going forward."

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David Smith, then managing director of branch accounting at the Post Office, also described Mr Bates as "unmanageable" in an internal document on the integrity of the Horizon system.

The document detailed instances where problems with Horizon were raised.

Referring to Mr Bates's troubles, the document said: "Bates had discrepancies... was dismissed because he became unmanageable."

Document delays

Current Post Office CEO Mr Read denied that the Post Office's repeated late submission of documents to the inquiry is an obstruction of the process.

Lawyers for the inquiry outlined a series of missed deadlines and broken agreements to provide documents in a timely manner so the material could be read, understood, and presented to witnesses.

Late disclosure in earlier stages of the inquiry was said by Jason Beer KC to be "highly disruptive" and the most recent delays were "very concerning".

The Post Office has said it "regrets" that documents were not disclosed to the Horizon IT Inquiry "as early as all parties would have liked".

A Post Office spokeswoman said: "We are fully committed to supporting the inquiry to establish the truth and we have disclosed almost half a million documents to date, reflecting both the unprecedented scale of the issues in the scandal and our commitment to transparency."