"ONS surveillance data suggested" - sounds like guess work to me. How did they arrive at that figure?. How many symptomatic/non-symptomatic individuals went for testing?. If 8 thousand plus were tested and found to be positive, it appears that, if the ONS figures are correct, I would suggest, a very large number of symptomatic individuals are not presenting for testing, as they have been asked to.
The system depends on people being tested and, if positive, also depends on them being contactable in order to supply their contacts, who, in turn, should be contactable.
The "independent" SAGE group is highly selective in the wording of its press release and is designed to mislead.
67% of positive testers were traced and then 85% of their contacts were traced, it's quite simple really and not misleading at all, unless, of course, you want to be misled.
I'm left wondering just how the approximately 15 thousand supposed "not traced new" cases, are to be identified, found and tested, if they do not present for testing. The same applies to their contacts. The "independent" SAGE group does not appear to tell us how.