Good tip re CAP413, there is a link to the CAA document
here.
Last year the CAA sent all commercial pilots a glossy booklet with standard calls from start up to shutdown, I understand they were planning a PPL version, but I guess that would only be sent out to existing licence holders.
CAP413 is a little overwhelming as half the RT calls are not relevant to a PPL, but if you can read through it, you'll soon pick up "standard phraseology" which is what it's all about.