Is it illegal to stand within 100 yards of the reigning monarch without wearing socks?
Failure to wear socks is just one of the fantastically bizarre range of claims made about British law which are examined and, mostly, debunked in the Law Commission’s Legal Oddities document.
Many, such as the socks, are not so well-known. A few, such as the legality of dying in Parliament, are widespread myths.
Hat-tip: @sphericalsquare.
If not wearing socks within 100 yards of the monarch were illegal, we would know more than we need to about the royal family’s intimate moments.
On the postage stamp question, I can rule that it is illegal to stick a postage stamp upside down on the envelope, but not to stick an envelope upside down under the postage stamp.