Unsure if this is national, but the Wilko by Nottingham Victoria Centre has around 20 Multiposition up to 55" TV Wall Mount Brackets marked down to a fiver in their clearance section.
It's this one: https://www.offerscheck.co.uk/tv-wall-mount-multi-position-32-55in/wilko/481486
Looks to be a discontinued item. Bloody well worth the money, I put it up this afternoon with my chunky old 50" TV and it's sturdy as a rock.
Also had the smaller up to 32" ones for a fiver.