I do now have more issues though that have arisen this morning.

stat was changed on Saturday and I did service at same time - oil and all filters - and all was fine, until this morning.
I forgot to mention in my post above, but the stat I took off was stuck open!

This morning, the EML light came on. Doing the pedal test it flashed 2 codes
0420
0597

I was told that a stuck open stat would not cause an EML light. Is that correct? If so, could the 0597 code just be an old code for the stuck open stat and now just needs clearing?

Also, an advisory on last MOT shows that there was a small hole in the flexi pipe on the exhaust (can’t remember exact wording). Could a small hole/leak in the flexi pipe cause the 0420 fault code? No idea when it comes to exhausts but hoping it’s not the cat