The R/T test is based ENTIRELY on procedures and phrases laid out in the CAA publication "CAP413 - Radio Telephony".
The book is released every year - with amendments. Next year, for example, will include the phrases "late downwind" and "fanstop" (neither of which are accepted as being in use at the moment - even though some do use them).
The book should be available from any flying school for £6.50
Would strongly suggest some groundschool at your local club before attempting the test.
I'll e-mail you some notes that should help.