I think you've brought up a lot of good points there, Jimmy.
The only thing I would say is we are unsure about the effiacy of the Oxford vaccine against the South African variant. The study you are referrring to when they talk about not protecting against mild/moderate illness was done in quite a young population apparently. The results for that study or the test on severe disease still haven't been published. I guess that begs the question, how likely would a surge in South African variant cases be in the UK if we opened up? And would all the people who have been given the Oxford jab (Pfizer have reported, in another yet unpublished study that their jab is protective) here be protected? It's an unknown.
I think they are shit scared of hospitals being overrun again. What is the wait list now for elective operations, for example? Last I heard was three years. That line of thinking may be right or wrong, but I reckon that's what they are guarding against.