OK retraced steps to the electronics store and found it's a Panasonic RP-HS35ME Sports Clip In-ear Headphones.
Removed the wires etc. from that so we were left with two over the ear "frames".
Prised one ear electrode (Tenspros,black 2mm plug type, they come in pairs) apart carefully to preserve the integrity of the part that connects the hinge and holds the spring in place.
Attached the electrode with a paperclip. Image 1 shows how the paperclip is used to attach the electrode to the ear frame. NB the 2 little black plastic "hoops" the paperclip wire is positioned through are part of the ear electrode and not the ear frame.
The red TENS lead is plugged into it the end of the electrode.
Image 2 shows the red electrode wires pushed into the groove round the top of the ear frame - where the original headphone wires were originally.
Wow! Superb! Thank you so very much! And excellent pictures. That helps alot! And this exact headphone is on ebay for <$10. But I'm sure any type with this ear frame will work.
Yesterday I thought of using similar earphones with frames and using hotglue to glue the electrode in. I hadn't thought of hotglue before.