If Fujitsu knew about the fault internally and failed to notify the Post Office, they are to blame too.

Whether they notified the Post Office or not though, the Post Office certainly knew. They not only shared emails about the problem within the organisation, they engaged in a cover up.

There’s a good BBC Panorama documentary on the scandal that was released more than a year ago.

I'm familiar with the case; it's obvious that the Post Office knew.

And the issue is not just that the Post Office knew, but that they were also in charge of the prosecutions.

Private prosecution itself is on trial here, IMO (IANAL but this opinion would not be unusual among lawyers from what I have read)

Edit to add link:

https://www.computerweekly.com/news/252485328/MPs-to-examine...

In Scotland the Royal Mail could not do private prosecutions and instead only did prosecutions via the regular public bodies - the procuratoer fiscal. So if the private prosecutions were themselves an aggravating factor, we'd surely expect to see a significantly lower rate of prosecutions in Scotland than in England? And the same goes for Northern Ireland

The data that I can see shows that 76 subpostmasters were prosecuted in Scotland which doesn't seem completely wacky out of line with the rest of the UK.

76 as a fraction of potentially over 900 nationally is disproportionately small, though I don't know whether there are disproportionately fewer sub postmasters in Scotland.

Do we know how many Scottish prosecutions did not go forward with the fiscal?

The fundamental issue here is that it is likely that the Post Office on the one hand knew of the problems with the code and on the other still continued its prosecutions (based on its longstanding reputation). The fact that in England and Wales they could get away with that without systematic scrutiny surely only sways the chances of cases succeeding elsewhere. There was evidence from Horizon identifying the frauds, after all, and they had been successfully prosecuted.

Scotland is 8% of the UK’s population. 8% of 900 is 72, so it seems exactly in line to me - as though public vs private prosecution made zero difference to the likelihood of prosecution.

Given the serious concerns raised about these specific private prosecutions by the House of Commons, perhaps there should be concerns about the legal system in Scotland then ;-)

Private prosecutions have to go - it's absolutely outrageous the Post Office are still allowed to keep this archaic power given the obvious conflict of interest and the total incompetence/corruption they have shown.

The Post Office has a number of special powers, grandfathered from when it was the monopoly communications provider in the UK (it ran both telephone and post). it was effectively an arm of government, that worked hand-in-hand with the security services. Their Investigation Division was responsible for steaming open letters and tapping phone-calls.

I imagine much has changed; but I'm quite sure that the PO is still not an ordinary business, like a courier service. They are an arm of government.

Well -- the Post Office now is an ordinary business (as of 2013 -- it is Post Office Ltd because they spun it off).

The bit that is not "ordinary" is Royal Mail.