Dougie
Expect to get a laminated sheet which acts as your map, a route and an information card with frequencies and information about different locations you can call enroute. You will probably be told about an enroute emergency that you'll need to make at some point, and perhaps some options on the type of emergency.
You'll be in a room on your own, with a headset and control pad to select frequencies. You'll get a piece of paper to scribble on. The examiner will be in another room and will act as the controller that you call. Expect to hear calls from other people too. What I did, was to write my details on the piece of paper which made responding to "Pass your message" easier!
You'll probably need to get an initial clearance to depart (as normal at somewhere like Prestwick), basic service ("pass your message" which you'll need to do a full response of), do a VDF fix (without getting a service from that place - one of my mistakes), do a mayday , perhaps a mayday relay, a zone transit, a MATZ penetration, get a clearance and land.
As others say - take your time - there is no rush. George will look after you!