1950s could be an interesting mix.
PVC sheath with polyethylene insulation
- FTE - sometimes power, more usually clocks
- FT - typically for lights
TRS, rubber sheath & rubber insulation
- FTE - power radials (no rings)
- FT - power, more usually fixed, separate earth wire
There was a rare FTE with the 3rd core insulated along its entire length in green. I suspect this was French or Belgium, black outer. It is solid core & non-tinned whereas all the other cable at that time and size would be stranded core & tinned. The benefit of tinned is corrosion products exclude oxygen where tinned contacted tinned.
Rubber is the best insulation and whilst physically very tough it is very nice to work with re flexibility at installation - contrast with BS7211 LSOH FTE where 2.5mm could really do with being stranded as it is not pleasant to work with. Rubber degrades at terminations, beware what appears sound may be cracked through to the cores to unwary fingers and since there is no CPC in some (FT) it presents a fire hazard as OverCurrent protection will operate rather than Earth Leakage (RCD).
I have been tempted to use 6-10mm H07RNF before now for cooker installs down twisting conduit with bootlace ferrules, however it's not worth the hassle. Tiles pop off easily enough if you do a thin plaster skim before tiling (the tile breaks away taking that thin skim with it rather than the tile breaking, soak overnight, scrape off, refit as need be). Likewise I would have liked to use FP200 red for smoke, but I hate silicone insulation as it is not very robust compared to "genuine" FP200 Gold from Prysmian whose insudite is much tougher to installation handling (does not nick or tear if you so much as look at it).