score:5
I was recently in the similar situation with planning a trip for my mum who’s a visitor visa holder.
I only followed the rules about requirements for entry concerning travellers from non red list countries including pre-departure negative test and booking Covid test package for day two and eight after arrival.
My mum was challenged at the airport for travelling during the pandemic while U.K. is in national lockdown. I was able to persuade the immigration officer that we were not intending to break any rules and was just following the official guides.
This may be seen as obvious with hindsight, however the confusion is caused by lack of explicit information by the government regarding certain visa holders in my opinion. I don’t think most people willingly want to break the rules!
After this I emailed both the consulate and the home office COVID unit and both referred me to the entry requirement for red list and non red list countries. They didn’t say she should not travel because she has visitor visa. This shows that there’s lack of clarity at government departments as well.
You may find this FT article useful though.
Personally, if I had been fully aware of the risks, I would have not planned the trip for my mum as it could have ended with her being refused entry after a long journey and jeopardising her future visits as well as application to renew her visa.
Best of luck