JdeBPThe relative has kept a non-kitemarked BS3283 kettle lead just in case xe might need it.
The relative has no working old electric kettles, and #BS3283 was withdrawn as an electrical standard three decades ago.
The lack of a kitemark implies to me that this connector has been hoarded since before I was born.
It does have the standard number embossed on the plug, although it is worn and very difficult to read.