Only side tank engines may use this column

Yes, they wouldn't want the fireman fried by the overhead cables, while standing on top of an engine's tender. It's those bits of railway history that photos like this record.
Those unfamiliar with railway practice can see what I mean at www.ipernity.com/doc/364457/26200415

Thinking back, it seems a shame that trackside fixtures and fittings were generally ignored by most photographers. But then again, we had much more variety of locos to point the camera at.

I agree - I made a brief and limited attempt to record some of the Somerset and Dorset structures still standing at Highbridge in 1969. The cattle dock on Highbridge Wharf was one and there a a few more adjacent to that in the album - www.ipernity.com/doc/364457/26460317