Regarding the whole home printer setup thing, can it not be set up as read only? I don’t know the technicalities in this I’m not that much clued up on all this tech but at least trying to understand it all.
No. There isn't anything that could be done along these lines. At the end of the day it's just a bunch of small dots on a page.
Movies and other content use a bunch of fancy tech like DRM and HDMI to protect the image right the way from the streaming company servers to your TV, but you can still get a very solid HD copy just by pointing your camera at the screen.
We don't have the same technology for protecting print, and introducing it would involve fundamental changes to the way printers work. Even if this was done and the document was somehow tamper-proof, you could pretty easily just scan it back in and modify the scanned copy.
What protects these paper copies is that there is qr code which contains the same information as is printed on the page. If the barcode is scanned and the information doesn't match, the person scanning it will know that you've committed fraud, which is a much more serious offence than breaching the restriction would be.
The qr code itself is signed using a government secret, and since nobody apart from the Scottish government has the secret, you can't just print your own barcode. Because of the maths used to create the secrets, it's possible to share a public code for each secret, which can be used by anybody to check whether the government signature in a qr code is valid.
All the validator apps have a big list of all the public codes for all the government secrets in Europe, so they can check any of the qr codes.
A couple of the secrets have leaked, but not from the UK governments. Where the secrets have leaked it would be possible to generate your own barcode and pretend to be from those countries. Since the reader app will typically tell the operator the country, and can be fairly easily modified to flag up if a barcode is signed by a leaked secret, it would be fairly reasonable for them to ask for some matching national ID from that country. Also again, if you are caught doing this, it is fraud which is a much more serious offence than breaching the covid restrictions would be.
In practice, if you can provide something which will scan, the majority of people won't give it a second glance and won't check it matches other ID, so you could probably just show a photocopy or screenshot of somebody else's pass. This would also be fraud etc...
None of which changes the fact that the whole thing is a monumentally pointless assault on basic rights, being forced on us by a morally bankrupt government on little more than a whim