There is no longer a PPL side to your ATPL. You may remember your ATPL of old stated that you could exercise the rights of a PPL on class A aeroplanes. This situation no longer exists.
What you need is a SEP (Single Engine Piston) or MEP (Multi Engine Piston) rating on your certificate of revalidation page to fly the respective types. Once you have this, you exercise the rights of your licence on these types whether it be for pleasure or profit.
To get this rating, simply go to your FTO (Flying Training Organisation) i.e. club of choice and complete enough training to take a Class Rating Skills Test, then take the test. The test now includes what used to be the GFT and the Nav test, but as a professional pilot you should be exempt the Nav element. On passing the test, you will be awarded the rating.
The rating now lasts 24 months (for the SEP). In the last 12 months, you have to have 12 hours in your logbook and an hour long flight with an instructor to be re-validated. If you don't have this, another skills test must be flown. The requirement for 12 hours on SEP types is not reduced by your professional flying.
All details are in LASORS, available on the CAA website.