As I’ve read it is in Norway.
My understanding is that whilst it is not technically a current legal requirement there is the looming issue of being sued. This can be assessed under the Equalities Act 2010 for non-compliance with the governments accessibility standards. This doesn’t however prevent everyone from perpetuating that it is a legal requirement and I, in fact, often say this to push the severity of not delivering accessible products.
WCAG and W3C are guidelines - not rules. But it’s a moral issue. Would you design a website that’s not usable by Spanish people for no other reason than laziness or your own styling choices?
There’s about 2.7m colour blind people in the UK alone and a further 2 million with sight loss.