Same here: zero chance that's going to be installed on anything I access, or my partner's kit.
The benefit to the NHS is having centralised data in order to do Big Numbers analysis of spread shouldn't be underestimated, but there is no trust there - they've already sold medical data to Google without a by-your-leave and despite many people explicitly opting out several times. And the "give notifications to people who are most at risk of having got infected, and not to people who are much lower risk" should kill it stone dead - who decides which participant is worthy or being notified?