I’M like a dog with a bone with this story – I know. But it wants forensic attention. On Tuesday last week, the Lord Advocate Dorothy Bain KC spent an uncomfortable hour in Holyrood, answering questions from MSPs about the Post Office Horizon scandal.

This is the first time the Lord ­Advocate has spoken publicly about the ­distinctive ­Scottish impact of the faulty Fujitsu ­computing system which implicated ­hundreds of innocent postmasters in crimes of dishonesty over more than a decade.

She finds herself answering these ­questions because in Scotland, it was the Crown Office and Procurator Fiscal ­Service which ran these cases.

South of the Border, the Post Office ­pursued its own private prosecutions, ­lodging indictments, cutting plea deals with the postmasters they were accusing of crimes, and offering them softer ­sentences if they pled guilty and paid over the “­missing” money into Post Office coffers.

Some of these deals were premised on postmasters agreeing for their defence ­lawyers not to mention Horizon faults ­during any pleas in mitigation on their ­behalf. In the paranoid world of Post ­Office law enforcement, postmasters had to accept being totally in the wrong even to plead guilty.

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In Scotland, the criminal side of this ­scandal worked differently. Here, the Post Office was just a “specialist ­reporting ­agency” – passing on incriminating ­evidence to procurators to make the final call on whether or not postmasters found themselves up before the sheriff accused of theft, embezzlement or fraud.

They could – and did – make civil threats against subpostmasters they reckoned owed them money, but they didn’t have the power to dangle criminal theft charges in front of desperate men and women in the hopes they pled guilty to false accounting and settle their phantom debts.

Last week’s statement represented Bain’s first opportunity to set out in detail what Scotland’s prosecutors knew about problems with Horizon, when they knew about them, and what they decided to do about it.

Some of us optimistically hoped that the independent check of external prosecutors might mean fewer people were wrongfully accused of theft and embezzlement here. Corroboration is often described as an ­invaluable safeguard against miscarriages of justice. Did it act this way in Horizon cases, resulting in uncorroborated allegations being discontinued? Till now – it has been impossible to say.

There are grounds both for optimism and scepticism in the light of what Bain (below) told MSPs last week. First, the good news. The Crown Office has revised down the ­number of cases potentially affected by the junk Horizon evidence from up to 100 to just 54.

The National: Lord Advocate Dorothy Bain KC

This holds out the possibility that – head for head – the proportion of Scottish subpostmasters wrongly prosecuted may still be lower in Scotland than in England and Wales – where the Post Office had its own indicting privileges. This is a cold consolation to those who were wrongly accused, but a little less injustice in the world is no bad thing.

The Lord Advocate’s statement left us in no doubt about who she considers the central villain of this piece to be. There is now compelling evidence that the Post Office wilfully suppressed evidence, lied to postmasters, lied to lawyers, lied to civil and criminal courts – even lied to Parliament. Adding Scottish prosecutors to the list of organisations the Post Office cynically deceived about the unimpeachability of Horizon should shock no-one.

Bain confirmed Scottish prosecutors were “repeatedly misled by the Post ­Office” and “assurances that were just not true were repeatedly given” to them that Horizon was reliable until 2019. ­Because of this failure in their “duty of ­revelation,” she said, postmasters were wrongly prosecuted in sheriff courts across the ­country “because prosecutors in Scotland accepted, as they were entitled to, evidence and explanations at face value from the Post Office”. They were, she argued, one of the Crown’s longest-standing specialist reporting agencies who COPFS were ­entitled to trust.

Which is fair enough – as far as it goes. But there was a second sceptical strand to Bain’s statement which sits uncomfortably alongside this image of an entirely innocent Crown Office, prosecuting in good faith based on the evidence they were handed.

Because COPFS is also angling for ­credit for its scepticism and caution about Horizon’s reliability. This has been obvious since January, when a spokesperson claimed that the number of cases prosecuted in Scotland was lower due to “policy ­decisions made in response to awareness of the Horizon system issues.”

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But answering questions from MSPs, the Lord Advocate insisted “the Crown Office and Procurator Fiscal Service was not advised of the deep and profound difficulties with the Horizon system” and “did not know about that until 2019”.

“Until such time as the Bates decision was issued and, ultimately, the Court of Appeal in England and Wales issued the Hamilton decision,” she said, “it is wrong to say that the Crown was aware of ­problems, did nothing about them and continued to prosecute in the face of ­reported problems.”

Reading this, you could be forgiven for thinking that the mysteries of Horizon were first revealed to Scottish prosecutors in 2019 and there was no knowledge of any system issues until then.

But the rest of her statement substantiated that this was not the case and the Crown Office did do a number of things about

Horizon before 2019 which are ­inconsistent with the idea prosecutors were ­completely clueless about potential issues with ­Horizon till Alan Bates won his major civil action in the High Court in 2019.

Bain explained that in “May 2013, the Post Office lawyers contacted the Crown to address public concerns” about the reliability of Horizon. She described a further meeting in August 2013 as being sought in “recognition of the continuing public concern”. She didn’t build on what prompted these “concerns” – but it seems likely this must have been contemporary reporting in different parts of the press about Horizon.

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I entirely believe that false ­reassurances were given to Crown Office lawyers at this meeting – and at the other meetings she identified in August 2013 and 2015 with Post Office figures.

But the fact these meetings occurred – and resulted in ­significant changes to prosecution policy in Scotland – shows that concerns about the reliability of Post Office systems in Chambers Street clearly did not begin with Mr Justice Fraser’s judgment in the winter of 2019 – otherwise why would Scottish ­prosecutors have sought several meetings and ­assurances from their Post Office counterparts?

And if they didn’t have some ­constructive awareness about the ­problems with Horizon until November 2019, why did they stop prosecuting postmasters using Horizon evidence some four years ­earlier?

If the Crown Office was completely in the dark about the problems with ­Horizon, why did it take the sweeping ­decision to effectively call in all Post ­Office cases to be reviewed by its most ­senior lawyers on October 20 2015, with a ­recommendation to crown ­counsel to “discontinue ­action, or take none, in ­cases that relied on ­evidence from the Horizon ­system to prove that a crime had been committed”?

This was a good directive. It undoubtedly meant that some people wrongly fingered by the Fujitsu data were not prosecuted for crimes of dishonesty in Scottish courts.

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But remember – this directive to kill off Horizon prosecutions in Scotland emerged from the Crown Office over four years before the High Court in England finally determined that the Post Office had been lying through its teeth in the Bates litigation about the known reliability issues with the Fujitsu system.

Parsing the Lord Advocate’s statement, I guess her position must be that until 2019, the Crown Office didn’t know for sure that Horizon was dodgy, but by October 2015, Scottish prosecutors couldn’t be satisfied it was reliable either. While maintaining Horizon was tickety-boo, Bain confirmed that the Post Office failed to produce an expert and expert report testifying to Horizon’s reliability.

There is, I suppose, a lawyer’s distinction you can draw between knowing for sure that an IT system is generating junk data – and being unable to say for sure whether a computer system was reliable. But many of you reading this are probably hearing the ­gentle tippy-tap of angels tangoing on a pinhead.

Either the Crown Office was the Post Office’s dupe, or it was a sceptical and independent prosecution authority which tested the claims made to it by its ­specialist reporting agency, protecting the public interest and Scottish ­subpostmasters from the Post Office’s deceptions.

Reading the Lord Advocate’s statement – with its strange narrative of ignorance and ­intervention to stop Post Office prosecutions proceeding – it sounds like COPFS wants it both ways.