Current protection scheme in tatters — need extremely qualified expert (4,3,5)

I believe the answer is:

test and trace

I'm a little stuck... Click here to teach me more about this clue!

'current protection scheme' is the definition.
(UK Covid-19 testing system)

'tatters need extremely qualified expert' is the wordplay.
I cannot quite understand how this works, but
'expert' could be 'ace' (ace is a kind of expert) and 'ace' is found within the answer.
This explanation may well be incorrect...

'in' is the link.

Can you help me to learn more?

I've seen this clue in The Guardian.

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