Im not from UK(Im from Slovenia) and order new
Cupra ST(Still waiting it) and there is also not option to have BSD&RTA ...
But there is way to add it as retrofit option as done and you can find on youtube videos...
You need to buy Master & Slave radar from golf(because have dynamics learning), Golf holders for radars, cables ... Then there are 2 options for notifications you can use normal 12V leds somewhere on dashboard or mirror or buy
Ateca mirrors with BSD LEDS integrated...
But retrofiting take a lot of time, you need remove rear bumper, align and fix radars(only 2 bolts match, third need to be modified), connect cables from radars to front car(fuse box and mirrors), reprograming ...