There aren’t many SUV available for £0-£500, so your choices aren’t that great. I’m of course talking about actual SUVs, not slightly raised hatchbacks (Mokka etc).
A new Sportage could be had for £499, Bridgend has a dealership (i should know, i’ve been there to take a Sportage for a test drive lol).
It’d certainly help if you give some pointers about needs. Big car? Small car? Automatic mandatory, all those things matter a lot when you’re looking at the low end of cars.
A good, reasonably safe bet would be the Citroen C3 Aircross (£395, best “small SUV” 2021).
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.