Best thing to do post-PPL is to buy a plane, or a share in one. Nothing will do as much for your currency and enjoyment of flying. On the other hand you may be one of the lucky few who can rent a very nice plane, in which case this doesn't apply.
Unless you are really not interested in going places, try to do the IMC Rating also; this will affect the choice of plane / share to buy because many cannot be used for training for a new license/rating.
Referring to how many give up and how soon, this data is not available from the CAA website directly but one can work out some estimates for 2000 and before. One needs to make some assumptions about the average age at which people start (that can be derived from the data) and the average age at which people give up. Looking at the data it's immediately evident that the total # of non-expired PPLs remains roughly constant while about 2000-3000 join every year.