Why don't you ask your parents, say something like I smoke weed but don't like going to dealers that also offers me crack and you don't like funding the black market or wasting your money on it,

You may be surprised by how cool your parents can be about it (ok mine weren't but friends parents were super cool about growing and shit). If your parents don't know you smoke you should tell them anyway because they'll be much happier hearing it from you.

You could also try a guerilla grow out door in a wooded area maybe a little late in the year now but you could get an alrite yield if you planted quickly.

Plus you're british I notice so it's unlikely they're right wing cristian nutters like you get in the USA (I know not all but theres a lot more) it's likely your parents have done a fair bit of smoking In their day and will understand.