I have lupus, take steroids and immunosupressants. No letter. In Wales they addres being sent or up until the 29th, and some from individual GPs.
I haven't been out for 10 days, I know how difficult it is for me to fight a cold if I'm run down.
I'm lucky though, I can absorb the cost of not working. If I needed evidence for my employer, with no letter I couldn't provide it.
Anticipating a letter next week, but don't intend leaving house/ garden regardless. Do what you can... everybody should be trying desperately to stay at home as much as possible atm anyway, health conditions or not I would have thought.