Have a look at the Safety Sense Leaflet on radiotelephony which can be found at
http://www.caa.co.uk/srg/general_avi...sp?groupid=231
Will give you a run through of what is expected of you on the RT oral.
You will fail if you mess up the Mayday, Pan Pan or relayed emergency messages but as long as you sound confident and have a practice session you will pass. Expect an airplane to break down on the runway meaning you will have to divert.
Walt,,