The origin of the Horizon system was actually a belief that benefit claimants were on the fiddle – though I'm sure the PO was happy enough to believe the SPMs were too.
The ideological belief that any of the UK's ills can be laid at the feet of benefit claimants seems to be perennial.
So in 1992, Peter Lilley regaled the 1992 Tory conference with his benefit-bashing song:
"I've got a little list
Of benefit offenders who I'll soon be rooting out
And who never would be missed
They never would be missed
There's those who make up bogus claims
In half a dozen names
And councillors who draw the dole
To run left-wing campaigns
They never would be missed
They never would be missed
Young ladies who get pregnant just to jump the housing list
And dads who won't support the kids of ladies they have ... kissed
And I haven't even mentioned all those sponging socialists
I've got them on my list
And there's none of them be missed
There's none of them be missed.
http://news.bbc.co.uk/1/hi/programmes/the_daily_politics/6967366.stm
And in the 1995 conference he announced the Pathway project to computerise benefit payments at the Post Office, which emerged as the Horizon software.
By 1999 the whole project was already known to be an IT shambles:
https://www.independent.co.uk/news/business/icl-stumbles-on-pathway-to-hell-1092947.html
NB It's worrying to note that, just a few weeks ago, we had the announcement of another mega IT project involving technology which provides no transparency to the accused, and with potentially serious impacts on entirely honest people.
This time it's the DWP using artificial intelligence to surveil the bank accounts of everyone receiving benefits, whether there's any case against them or not.
DWP to surveil bank accounts of benefit claimants for fraud
https://www.computerweekly.com/news/366560856/DWP-to-surveil-bank-accounts-of-benefit-claimants-for-fraud
https://www.theguardian.com/politics/2023/sep/03/uk-warned-over-lack-transparency-use-ai-vet-welfare-claims
Ministers have maintained a veil of secrecy over the system, which the transparency campaign group Big Brother Watch has described as “seriously concerning”. The DWP has refused freedom of information requests and blocked MPs’ questions, arguing that providing information could help fraudsters.
Even the FT is unimpressed with this new government IT project:
UK move to curb benefit fraud triggers privacy concerns
https://www.ft.com/content/31f548bb-e0d6-4167-9c09-ce4f4d590386