Does anyone know where the outside temp sensor is on the new Octy? Mine's gone a bit dicky and I want to check it's just not a simple loose connection before I fire it back at the dealer

Maybe in the same place as Fabia, which is down on the N/S lower grille of the bumper.

Pull out the grille & the sensor & wiring can be examined.

and in case anyone was wondering what the problem is. This was on my way up the M1 last night and it was bright, dry and warm

A friend with a Toyota Rav4 had exactly the same problem; sensor had died. Behaves fine now.