I don't know who succeeded DP Davies directly, but I've worked with several CAA CTPs. The last of them was Paul Mulcahy - last because despite very little real flight test skill within EASA and some obvious imperatives to maintain a national skillset, Andrew Haines the then CEO decided late 2013 that CAA did not need a flight test department and made them all redundant. Paul is now project test pilot for the PC24 at Pilatus; his predecessor was Jock Reid who was in post circa 1997 when I first started working with that department, but I don't know for how long before and who preceded him.
I can't see Jock in any of the usual directories, and hadn't heard from him for years, so have no idea if he's still alive, I can only assume he's not in any kind of professional practice any more, which would be unsurprising given he must be 70++ now.
Presumably as we leave EASA this will be one of the various skillsets to be re-established: hopefully one of the excellent Brits at Airbus Toulouse or BAe Warton can be persuaded to take the role, or even Paul himself although he seems extremely happy in Switzerland.
G