I’ve used Camskill Tyres and they're usually very good price-wise. Delivery service was also good. They are supply-only so you’d need to find your own fitter. Website;
https://www.camskill.co.uk/
Like @OomStu_ZA I’d also recommend Michelin. I had Michelin PS4 on my 2020 Polo GTI+ (I no longer have the car) which, like yours, had 18” alloys. If I still had the car and if it needed new tyres, I’d go for Michelins again - probably PS5.
Prices on Camskill are;
OEM spec; 215/40 R18. Load index / speed rating; 89Y
Michelin PS4 - £126.80 incl VAT
Michelin PS5 - also £126.80 incl VAT
225/40 R18. Load index / speed rating; 92Y. Some owners fit this slightly wider version as they’re a more widely available size, so cheaper than the OEM spec tyres. Prices;
Michelin PS4 - £95.05 incl VAT
Michelin PS5 - also £95.05 incl VAT
It’s worth also checking out the Black Circles website (
https://www.blackcircles.com). Michelin own Black Circles so often run money-off promotions on Michelin tyres. Asda Tyres (
https://www.asdatyres.co.uk) can also be quite competitive on tyre prices.
Over the years, I’ve read on various forums of a number of tyre fitting places damaging customers’ diamond cut alloys - either caused by inexperienced / over-zealous tyre fitters or poorly maintained tyre fitting equipment - and then deny they caused the damage. I’d guess the cost of a top quality professional refurb of an 18” diamond cut alloy to OEM standard probably costs in the region of £175 - £200 these days, so with this in mind, I’d recommend that wherever you go to get your tyres fitted, you get them to agree the condition of your alloys before they remove the existing tyres / fit the new ones (worth taking photos of your alloys beforehand so you’ve got proof of their condition).