Apparently Brownell’s UK sells molds (ahem...moulds) but the variety looks limited. My guess is that something as unusual as a .41 Long Colt mold can’t be found, but is legal.
https://www.brownells.co.uk/Reloading/Bullet-Casting/Casting-Moulds/Handgun-Moulds
Yea, Brownells in the US is pretty limited when it comes to moulds, too. However, there are other places (3 or 4 in the US) that make them. Without a CLEAR answer on whether or not it is legal, I am glad I did not send it.
Isn’t there a government list somewhere in England where they list what caliber and/or gun is legal and what is NOT legal? If not, it would seem that anyone from any little podunk place could outlaw anything they want to. That is why “shall issue” instead of “may issue” is so important with concealed carry licenses in the US (I have one and use it).