Re: Suggestion...
Not Serco though; this is a popular myth now widely debunked. I believe they have a lot to do with the manual tracing programme but not the app, which is completely separately operated (to the chagrin of the government).
Officially, the following were involved with the app:
Accenture, Alan Turing Institute, NHS Digital, NHSx, Oxford University, VMware Pivotal Lab and Zuhlke Engineering, plus the National Cyber Security Centre.