From a large picture book on the history of all things in Britain / England / the UK, there is this old picture of a roof-top structure on an exchange building. Dated about 1910 and all the insulators are on steel "J" pins. The insulators seem to look like the red Bullers profile. The lineman must be confident in the ties, as one guy is shown laying down crossways on the lower wires. Looks like a steel structure, no wood used that I can see.