first of all you will need a class 2 medical in the UK , next you will be up for :
1. air law exam
2. human performance exam.
3.english language proficiency test, can be done on flight test or before with an examiner (make sure examiner can sign it off some can not)
4.radio exam can be done at the same time as PPL skills test, but make sure examiner can sign it off, some can not
you will need to have an least 100 hours of flight time as a pilot.
for your aeroplane class rating at least 100 hours in class and pass a skills test , can be done whilst conducting PPL flight test.
Your night rating will be transferred over "free" on licence issue.
you will need training as required by the ATO, there is no minimum or max for PPL
Your licence will need to be current and your aeroplane endorsement will need to be current
your better off to get your part 61 licence before conversion than having your car 5 licence.