I have similar concerns as a principle. On balance, I most likely will use the app because if I should contract the virus and be asymptomatic then at least anyone with whom I will have come into contact can be made aware and protect themselves and others.
But first I want to understand more about security, how the data will be stored, how long for, how it will be used, who will have access to it etc. Is there going to be legislation to set parameters around how government can collect, store and use the data - and time limitations when they will stop, even if an app is still installed?
Thousands of people need to be trained up as tracers, going out and talking to people who have been identified as being in contact (whatever that exactly means) with an infected person. What checks and safeguards will be in place?
This is where I expect Labour to be asking questions. I can see the difficulty as it will be too easy for them to be accused of being obstructive, not helping the government lift the lock-down etc., but it is important that the government is subject to very high scrutiny over this. A lot more information is needed imo.