If you are in contact. as in the same address, as someone that is positive then you have to isolate for ten days. The NHS app pings and tells you that. The UK prime minister was caught out by this last week and said he would take a test everyday instead of isolating but there was an uproar against himself skirting the rules that everyone else has to abide me. Boris is currently isolating.
There is no doubt that this decision was made because they could stop performances for ten days but then what if there was another positive result. They can’t keep doing that. I am not sure why things are different for his production of Joseph that is going ahead though.