Oops.

That said, if you didn’t notice it when you cleaned the car James it’s probably not super obvious to see.
Is it just a slit or a flap that can be pulled?
If it’s a slit then open it up gently to see how deep it is. If it’s not through to the inner then it’s legal to use, and if it’s a flap it should be easy to see how far through the rubber it’s gone. Personally I’d tidy it up with some puncture repair glue and keep a close eye on it for further deterioration. Not wishing to teach anyone to suck eggs here if I’m stating the obvious.
Might be wise to put it on the back to reduce weight/stress loading a little if the tread depths between front and rear aren’t huge, or just swap both pairs front to back and vice versa.
If they’re quite worn already then maybe just keep them in the front and wear them down over winter. Chances are, as autumn and winter set in, potholes will proliferate and there’ll be the odd further unavoidable impact - better to do that with an older tyre than risk knackering a new one.
Hankooks on mine from the factory too, and they seem ok but like Watts and davo I’ll likely be looking elsewhere at replacement time.
davo245, interesting to see you prefer the PS5’s - what areas do they stand out in that brings you to that conclusion (other than the velvet sidewall 😁) ? Genuinely interested being as Michelin do quite a range of performance tyres so each version must have its own USP.
I ran PS4S on multiple former cars for quite a lot of miles so always interested in something that’s better for daily use.
In my eyes a car used in the UK and Ireland needs bloody good wet weather performance above all else.