Well George Allen - thanks for you faith in me, here goes.
Bottom Bracket shell, Ilkeston. A milling machine was set up to gang mill the 4 slots.
Seat Bolt, definitely Ilkeston. These were threaded 8mm with very shallow heads left proud of the seat lug ears. I believe Ilkeston was the only builder to use these
Rear Brake Bridge - Ilkeston
Frame Number SB 1015 and the size of the figures matches the number stamps used, plus the size stamp 56 - Ilkeston.
Wagner crown used at Ilkeston , but a lot of builders used these
Chain Stay Bridge - Ilkeston. Usually cut from the top of a seat stay.
Drilled ends - Ilkeston. Incidentally the drillings adjacent to the rear adjustors were "blind" and very shallow so as not to weaken the ends.
The finish as someone remarked (can't remember who) very much C&G of Liverpool. The gold lining of the eyes very much a trademark of theirs.
Oversize seat stay caps may have been filed flush. BUT no holes in the head tube where the Heron badge was fitted which leads me to believe they were filled on on refinishing.
George Allen spot on with the 801 & 803 classification and seat pin size. 801 27mm & 803 26.8 mm. Both metric OD's the 801 being the thinner.
Final opinion - An Ilkeston Frame which has been refinished