So, I had to jam it back in using a mix of wire and JB-Weld, to try and get a reasonable seal.
I took it for an MOT once, and it failed on emissions being too high. While the MOT tester had it hooked up to the gas tester equipment, I temporarily disconnected the injector to the cylinder with the dodgy plug and voila - the emissions level dropped to a pass level. He was amazed, and badgered me to reveal what it was I had done. Reluctantly, I told him, and he gave the car a pass certificate, knowing full well I'd be reconnecting the injector as soon as I'd left the garage.
Surprisingly, the engine would run fairly well on 5 cylinders, and didn't sound much different at low engine revs.

