...if you received your vaccine outside of the UK.
www.independent.co.uk/travel/news-and-advice/test-trace-flight-foreign-vaccines-isolate-b1941749.html
My mother currently visiting from an EU country where she lives was flagged as a contact of a positive person (someone on the plane) and has to self isolate, even though she received their jabs well over 14 days ago and has an EU Covid passport. Basically, Grant Schapps considers her vaccinated so she didn't need to self isolate upon arrival, but for Sajid Javid she's unvaccinated and has to self isolate now being flagged as a contact.
It's mind blowing that she and I could've travelled on the same plane and been flagged as the contact of the same person but she would have to self isolate and I wouldn't, simply because I got my vaccines here.
However, she's allowed to break self isolation early to go to the airport and catch her flight home and is under no obligation to do a test to prove she's negative before she breaks self isolation.
There is no logic in any of that except stupid obsession with exceptionalism which is so frustrating.