Assuming you're talking about the genuine Seat tick lights and not aftermarket ones...
They're direct fit if you get the correct UK spec inner light units. The LHD market ones have the fog and reverse lights on the opposing sides so you'll need to re-wire the fog and reverse lights if you get European spec ones.
The BCM needs dealer coding though otherwise they will flicker. They have an adaption on their software for retrofitting the LED rear lights but third party coding tools don't have this.
The coding process is detailed in TPI 2026910/1. You might need to give that to the dealer if they're not sure what to do. They'll probably charge you half an hour of labour for the coding though. I think that's the smallest charging unit they have for labour.