No in the UK, if you do not pay a building contractor, court gives builder permission to "recover their goods" which is demolishing it.
Designer seems to have recovered his goods domain/hosting and used it for what he wanted. To slag off the debtor.
BTW, I don't know why everyone assumes the facts are as described on the defaced website. It's not like we've heard the other side of the story. (Personally, I'm unlikely to spend any time to study it in detail, anyway). But if I knew who the web designer was, I'd certainly stay the hell away from him. This was ridiculously unprofessional and inappropriate.