Paul

First Direct, I forget its actual name, Ive had it for well over 20 years.
Its basically like a bank account with a huge overdraft, I can pay in, or take out, as I please.
They charge monthly interest (only if my linked main account goes below £50). The only requirement is its cleared by my 65th birthday.

[ You cant get them anymore, although they still do something similar, but the requirements for those are out of my reach ].