I don't know about over in the UK, but over here it's still a free country.

That's why we have so many laws: If something is not specifically forbidden, than it's A-OK!

Seroisly though, what's wrong with wearing socks with sandals? The idea of sandals is to be comfortable, so if your comfortable wearing socks, do so. If not, don't. Don't obsess over what others are doing or wearing.

In short:

MYOB!