I think you’ve hit the nail on the head - it matters whether it’s permanent.
Technically, somebody with flu’ might not be able to get out of the house, but obviously this isn’t going to get them free prescriptions for life.
I’ve no idea what the exact wording is, and too lazy to Google, but I think, in effect, your doc would have to certify that this is likely to be permanent. It’s probably a bit premature for that yet. I doubt that you are never going out again by yourself, even if you haven’t for a while. Really, there aren’t going to be that many people it applies to, as many people in wheelchairs still go out independently.
There are some here whose GPs have turned a blind eye to the exact letter, and signed an exemption form anyway, but they’re certainly not obliged to, and I know, speaking personally, I’d feel awkward about putting my doctor in a difficult position by asking - if nothing else, she knows I visit her (albeit rarely more than once a year), and I don’t turn up with a carer, so it’s pretty obvious I can leave the house. I can’t really ask her to pretend she doesn’t know that - even if there’s a possibility she might play along.