Like most here, I'm on a few forums and there are always some people that ask for information /confirmation after receiving some hearsay and no matter what evidence you give to validate the truth either way, they always keep coming back with "but I was told it's xyz" or start another thread asking the same thing. So I can sort of see RK's stance. :?
Long dropouts, over bb guides, plain lugs, italienate seat stays sort of point to early - mid 70's. Loads of builders could have made it. Back in the 70's most GB frames were white
More recent post says better Butler frames were Roberts sourced which was also my understanding? Pearsons in Sutton also used the Croydon framebuilders but would also source from Dave Yates so who knows.
The frame number on the drop-out isn't that common, that must narrow it down somewhat?