Yes - you are credited the theoretical knowledge requirements for the PPL(A), by virtue of having passed the ATPL(A) examinations. See LASORS C1.3:
The holder of a valid pass in the former professional UK Navigation and Technical ground examinations (Aeroplanes) or the JAR-FCL CPL(A) or ATPL(A) examinations will be credited this requirement.
(Applicants who have taken and passed the Flight Engineer examinations may not claim this credit).