You must isolate if someone in your household has had a positive test or is symptomatic.
If someone in your household has been asked to isolate by NHS Track and Trace, but they have no symptoms, you do not need to isolate. However, you must have as little contact with them as possible, and cannot have visitors to your home until their isolation period is complete.
If they develop symptoms, you and the rest of your household must isolate for 14 days from the onset of those symptoms.
More information on Track and Trace is available on the NHS website.