In EASA (it might be different in the UK) you may fly a 747 with a PPL provided you have the type rating on your licence.
To get the type rating, you need a multi engine IR, an MCC and advanced UPRT training.
The ATPL(A) theoretical is mandatory for multipilot aircrafts(FCL.720.A (b) (3))
So compared to the traditional training route for airline pilots, you save 15 hours of training for the CPL, and you only need a class 2 certificate instead of class 1.