There we go, in the UK:

Section 14(1) of the Wildlife & Countryside Act 1981 makes it an offence for any person to release or allow to escape into the wild any animal which is of a kind which is not ordinarily resident in and is not a regular visitor to Great Britain in a wild state.

So in principle you could be prosecuted if your snakes escape by accident because you hadn't taken the measures necessary to prevent them from escaping. I'm not sure how heavily the law is enforced, one snake you'd probably get away with, but freeing 20 babies may be pushing your luck.