So on the 10th November, John Penrose MP, husband of Dido Harding was told to self-isolate. Yet Dido was only informed by her app 5 days after she was in contact with someone (14 days self isolation, 9 days left when notified). So presumably hubby wasn't the contact. Good illustration of how weak "her" system is, that she can wander around for 5 days as a potential "spreader".
Penrose was told to isolate because he had been in contact with some who had had a postive test. Penrose himself has not had a positive test.
People who live with those who are self-isolating but who haven't had a positive test don't have to self-isolate. Therefore Dido didn't have to self-isolate just because her husband was.
She herself has subsequently come into contact with someone who has now had a positive test. So now she has to self-isolate.
Those are the rules, and I am sure that they were laid down by the Government's medical advisers, and not by her.
If every contact of someone self-isolating had to self-isolate, there would be no staff in hospitals or schools.