Right then. 2 parts:
"COUPLING PIECE" part no. 1J0973702 £3.48 inc VAT
"WIRE SET$" (that's what it says on the invoice!) part no. 000979131E £3.50 inc VAT
The wire is just a single conductor, terminated with a contact at both ends. I could have bought a corresponding red wire, but since there's no polarity to worry about, I'll just cut the yellow one I have in half and use both ends. It looks like the contacts are to be inserted in to the plug, then by pressing on a purple piece of plastic which slides within the plug the contacts are fixed in place and prevented from popping back out. If you want pictures, just Google the plug part number for images, there are plenty.