The Friends of the NRM started to publish a series of comprehensive books on the 'History and Development of Railway Signalling in the British Isles'. The first volume, 'Broad Survey' by Stanley Hall (ISBN 1 872 826 12 1), was published in 2000. The second volume, containing essays on Absolute Block and Single Line working, followed in 2001. Unfortunately the leading author then died and so the series progressed no further.
Volume two would probably not be of much interest Simon - but it might be worth you looking at the structure adopted by Hall in volume one.