I'm a bit puzzled as to why the convention seems to have developed that when people talk about "worked by Absolute Block", they assume such working can only be done on double track or multiple track lines?
A while back, I did some background reading on the development of block working, and the efforts of the Railway Inspectorate officers to persuade railway companies to adopt it, culminating in the Regulation of Railways Act, 1889.
What came out of that was that, when the Railway Inspecting officers talked about block working, they meant that only one train should be allowed into any one section at a time, and that until that train had cleared to section, no other train should be allowed into that section. I was unable to find any reference, either in books written by members of the Institute of Railway Signalling Engineers, nor in references to the 1889 Act, which mentions the number of tracks.
Further, if you look at the way railways operate, from the WCML right down to a miniature railway in a park, giving children rides for 50p a go, every one of them operates on the basis of Absolute Block - i.e., never more than one train in a section at a time.
I grant you, there are an abundance of different ways of achieving compliance with the 1889 Act; automatic signals controlled by track circuits, trains having to be offered and accepted using BR penguins or their earlier equivalents, tokens released by the signalman at the other end of the section, and so on and so forth - right down to 'one engine in steam'. All of those methods, regardless of whether there are two or more tracks or only one, meet the essential requirement laid down in the 1889 Act for trains carrying fare-paying passengers - only one train in section at a time!
So why is that so many people (including the Signals Inspector on a large heritage line) try to tell me that "Absolute Block can only be worked on multi-track lines!" ?
As I see it, there are only two fundamental systems of working; Permissive Block, which can only be used on lines which never, ever carry passenger traffic (not even occasionally), and Absolute Block, which the law insists has to be used on every passenger carrying line, even if the train being worked is a goods train.
Mind, I'm open to correction. If anyone knows of an OFFICIAL ruling or law which says absolute block is a term only applicable to multi-track lines, please let me know. Up until now, I've never seen one.