The Prime Minister wrote to me. I don't understand why person C ends their isolation on day 14. Surely they should remain in isolation until 14 days after person D displayed symptoms? Can anyone explain why person C is presumed immune/not infectious during person D's illness?

Even if person d didn't exist, c should isolate for 14 after B is symptomatic. This just appears to be completely wrong

I think the way to look at it is thusly:
If you had this information about a household of carehome care workers, would you be happy with Person C looking after your gran on day 15?