It's a Lucas 45 starter with the solenoid attached to it.
The solenoid earth is attached to the starter by a copper connector. On the positive there is the main battery connector, wire from the alternator, wire from ignition. There is also a spade connector connected. It's the only spade so it must be right.
My only suspicion is that when I took the solenoid out that I might have pushed the fork type connector in the starter forward as I was lifting the starter motor out.