The BritRail map below shows all the regions covered by the different passes. This will help you to narrow down which pass to purchase.
BritRail Pass: All colour zones. Travel all England, Scotland and Wales.
BritRail England Pass: Light-blue and grey zones. Travel around the whole of England.
BritRail London Plus Pass: Grey zone. Travel in the South East of England and out as far as Stratford Upon Avon, Bristol, Bath and Cambridge (grey zone)
BritRail Spirit of Scotland: Green, purple, and pink zones. Travel around all Scotland (includes many ferry routes out to the islands).
BritRail Central Scotland Pass: Purple zone. Travel between Glasgow and Edinburgh via istorical towns such as Stirling, Linlithgow and Dunblane.
BritRail Scottish Highlands Pass: Pink zone. Travel around the Scottish Highlands by rail. Includes some ferry routes.
BritRail South West Pass: Yellow zone. Travel from London (including Heathrow) through to the South West of England, including Cornwall and Devon.
(If you are unable to see the map here, you will find the PDF available for download below.)