Thanks to ALL for their help. I think it most definitely the larger imperial.
So apart from the obvious thing that I need to buy a pair of calipers
Can I get away with reusing this cable - do I have to replace it under the regs ?- it does actually fit my new cooker switch, so if I reuse it all I'll have to buy isenough 10mm to go from the switch to the connector to the cooker.
So apart from the obvious thing that I need to buy a pair of calipers