Local authorities are prepared for another year of dealing with covid at least. The Spanish flu took 3 years before things started to settle, modern technology means we should get a handle on it a bit quicker doesnt mean to say we will.
Lockdown looks set to be in place until 31st march but no one knows when in march things may ease (even boris probably doesnt) , and what that means.
They dont know what protection the vaccine gives, with only 5 months of data it's impossible to know and Not everyone will be vaccinated by April. (Let's not get into the anti vaxxers)
Yes over 70s can now be vaccinated however in areas which have an older population they are still trying to get through the over 80s, also some areas had delays in getting the vaccines, so not everywhere is up to speed and if backlogs start its takes a few weeks to then catch up again.... if they can .
Government will want to open the economy again but I strongly suspect many areas will be tier 3 and potentially stronger measures in other places at higher risk.
Personally I would defer to at least end of june/july at the earliest so you can enjoy the experience more than you would in the spring.
But then it also depends on how worried you are about covid and the risks of catching it and not much being open as a result or not as easy to freely go to restaurants etc without pre booking
Harry potter is great but it is mainly indoors and you inevitably end up near people as you are all looking at the displays.
Hope you have a great time whenever you go op