BMK 685 - Overdrive Relay
Unfortunately this part has a date code which is later than the build of my car, so if anyone has one for sale (working or not working, as long as the case is in good condition!) with a date code of 3 65 or earlier then please let me know.
The OVERDRIVE RELAY sticker to the top of the relay was clearly produced as a roll of tape, hence it has serrated edges.