Did some testing - answered my own question.
1) Create attribute called LongLat (or whatever you want really)
2) Enter your co-ordinates like so: 53.305012, -1.730040
3) Edit the form and use the LongLat attribute instead of Postcode
You can get the Long Lat for anywhere with pinpoint accuracy by using Google earth, zoom in close, position your mouse at the point you need then read off the numbers at the bottom of the goole earth screen
Cheers Mo (Happy man today)