I first saw this pole a few years ago and I've always suspected the insulators were the Knob or India pattern.

Today I finally took a picture and they are indeed what I thought they were. They are shown in Bullers catalogs as E.I.560 but I don't know the U number. In the original picture the bottom left piece has part of the embossing visible and the R tells me that it was BR which stands for British Rail. This makes it post-1948.

To see six apparently intact examples on a pole is a spectacular find these days.