This seems as good a place as any to add a link to some rail information from fellow Brit Sam Hallas:

http://www.samhallas.co.uk/telecomms.htm

Under the "Railway telecoms" section there is some interesting information about various phone and signaling systems from the past. Also, go to the "Document repository" section and you can find some more railway telecom stuff plus some articles about level (grade) crossings.