That looks like rubber T&E but the CU appears single pole fusing so I'd say late 50s, much older you'd have double-pole fusing & much later PVC cables.
If there are white pads behind the fuses be careful, these old CUs had asbestos pads inside.
As an aside I once worked in a house with a similar looking cut-out, my "spider-senses" were tingling so I opened it up and found twin BS3036 fuses, 60A on Line & 30A on Neutral, somehow it was missed when they replaced the neutral fuses with solid links...