Exeter is at about 3.5 degrees West, so with your dish at the 0 degree position set your reciever to recieve France 2 on 11590V 20000 2/3 (this is on Atlantic Bird at 5 West). Align the dish , peaking it up with the analogue meter. Give the dish a nudge a couple of degrees to the left (on the mounting). You may need to increase the elevation a touch so that 5W is still on the arc. With a bit of luck you should be able to send the dish around to 28.2 East and 30 West to tweak your alignment.
The main things to get right for a good installation are that the mounting pole is perfectly vertical, the dish is pointing in the right direction, and that the inclination/declination angles are set correctly.
If you can afford it the Horizon HDSM is an serious bit of kit. I have two with special hex files for BBC1, 2, ITV, 4 & 5 and it just pee's over those crapy buzzer things. They are easy to use and you can download from their site almost any sat/transponder or they will write you a prog. They are also go for vsat stuff which i do loads.