All,
As per my previous posts on this:
TLDR
Jan(ish) 24
MIL light on; codes say post cat sensor U/S.

April 24 replace post cat sensor from MGOC. MIL disappears.
May 24, MOT time arrives; fails badly on emissions. New cat (one sensor and cat from ‘Bitz) and BOTH sensors (second sensor ordered by tester from unknown company) replaced by tester to get through.

Now got MIL back with code P0420 - Cat not performing too well (or words to that effect).
see the attached live data from last journey with MIL lit.
Your thoughts on the way to resolve this issue would be greatly appreciated.
Cheers,
Michael.