From memory, there were lots of questions relating to Mayday & Pan calls. Make sure you read these sections of CAP 413 very well as there are lots of easy marks to be had. (You need to make sure you get the easy marks as there are also some obscure "definition / semantics" type questions which seem to bear as much relevence to R/T as most of the Aviation Law exam questions had to that subject).
Otherwise go through CAP413 and make sure you know the differences between ATC, FIS & A/G and RIS & RAS services and the content of position reports and "Pass your message" calls.
As said above, everything you need is in CAP 413.
(For the practical exam,the Safety Sense leaflet on R/T is very useful as it gives example flights which are very similar to the ones you will be given, in terms of content & structure).
Good Luck,
Mr. W