PHE guidelines are that if you have been in contact with someone who has symptoms (under 2m for 15 mins or 1m for any time) then you self isolate until their test results come back. If they come back positive then it’s 14 days from the contact, if they test negative then you end your isolation. If you need to get tested yourself and it comes back positive then your isolation is reduced to 10 days.
Yep I’m amazed not everyone knows this yet !!!