Apologies if this is old news to everyone..........
After last trying in 2005 and being told by Network rail that they were "not in a position to provide members of the public with drawings or records" and more recently trying the search facility on the network rail archive website, but to no avail, I was extremely pleased when a request via "ask the archivist" provided me with a link to order (via their print facility) all the extant drawings for Singleton that had originally been in "The Plan Arch" at Waterloo.
Full marks network rail! (They have obviously realised this can be a money spinner for them!)
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