Thanks Pharg for your reply.
Interesting that the site you linked to in its explanation of O2 sensor operation stated that the post cat sensor should be some reasonably stable value. Other sources state that it should oscillate as per the pre cat. My confusion continues having seen both types of traces from the post cat - the one above recently and the oscillation when it was freshly replaced.
Anyway I’ve just had a 40 odd mile blast and there was no sign of the MIL. I’ve also made a note of the mileage it came on at the other day, so I’ll see if what the mileage difference is if it returns. Some sources have mentioned around 100 miles and/or a few start stop cycles between the MIL showing itself. All in all it working perfectly so I can’t see what the problem is (famous last words….).
Cheers,
Michael.

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