The percentage Dave posted (and where they changed the counting method) was close contact tracing. Im not an avid Mirror reader but here’s a link (first google result)
The privatised service now counts an entire household as being traced once one member has been contacted
www.google.co.uk
My additional comment was separate and about number of people fully self isolating ie what’s the point in us spending vast sums tracking and tracing and then people don’t isolate anyway. Probably wasnt clear but think both points are correct