In the UK, at present, there is no concept of an aerobatic rating or qualification that can be attached to a PPL - in order to compete in BAeA competitions you need to be signed off by the BAeA to compete at any of the various levels, but this isn't in any way associated with your license. The AOPA aerobatic course(s) offer an excellent framework for aerobatic instruction, but again, are not associated with your license.
There are moves afoot for EASA to introduce aerobatic ratings, but I'm not sure how far along that has moved.
No-one is going to let you hire an aerobatic type without being sure you are competent to bring it back in one piece, and if you can't point to a reasonable amount of verifiable aerobatic experience, you're not going to get far.
The bottom line is provided you get the correct tuition, there is nothing to stop you flying aerobatics in a suitable rented type, but you will need to devote the appropriate amount of time and resource to the training first.