Read LASORS on the CAA website, don't get too bogged down on all the details though, they'll provide training for that, It takes about 18 months to become a Licensing Officer display as good an understanding of the different types licence and requirements as you can.
A basic overview,
(N)PPL PPL restricted to UK FIR
PPL - Private flying, no remuneration, can add a night rating and an IMC (instrument flying)
CPL - Commercial flying, right hand seat of Multi-pilot, command of single pilot, flying instructors etc.
ATPL - for left hand seat in Multi crew aircraft.
Issued for
Aeroplanes
Helicopters
(There is no ATPL for the following)
Balloons
Airships
Gyroplanes
Microlights
PLD also does Engineer Licensing (JAR66 and Section L) Plus I believe they do Air Traffic Licences now, but i'm not too clear on these.
Hope this helps and good luck. It's a very good place to (have) work(ed).