There's also huge amounts of UK Govt infrastructure code available online and open source. For all kinds of things, from all departments.

You could pretty much spin up the code needed to run the boring bits of a country out of open-source code. How about the application for booking secure prisoner moves? [0] Or some nice open source security guidance? [1]

And that's just one department, most others are similar!

[0] https://github.com/ministryofjustice [1] https://github.com/ministryofjustice/security-guidance