Okay, bit of a U-Turn. The BB serial number has been staring me in the face... can't believe I didn't notice. The '0' also has a '1' stamped across it... making a 'Q'...
So not 02503. Q2503... A Harry Quinn frame!
Again, thanks to Tony on the CTC forum for spotting that. I was thinking just last night that I need another eyetest.
Going by the other serial numbers around mine, the Quinn registry on Classic Rendevous would date it to around 1963, which is in line with the original components it has. So perhaps it was built by Harry Quinn, then resprayed and built up with new wheels in '71 by Alan Richards and stickered as Tower Cycles.
I may be completely wrong. But rather exciting stuff either way!