I think it is a switch, rated for mains voltage - not a relay hence the link I posted above.I'm puzzled. It claims to be mains voltage - 250v AC. Why would an engine need a mains relay?
Yes there's one on UK eBay
1pcs SCHLEGEL IEC60947-5-1 IEC 60947-5-1 T70 5E4 250V 6(3)A CONNECTOR 4 feet | eBay
Thanks to all, have found UK outlet.
Something to do with the engine starting on a Princess 360 with pair of 63 P engines.