Injector issue

[Roger Irrelevant]

Hi
Driving home last night, my otherwise well running little car started running badly, felt like it wasn't firing on all four cylinders.
I did the easy and obvious, and replaced the spark plugs and a very dirty air filter but no change.
So I disconnected the injectors one by one while the engine was running and as expected with each disconnection the engine stalled with the exception of cylinder three. Next I swapped the injectors themselves around to see if it was a clogged or faulty injector and found that regardless it is always the same cylinder, No.3, that is at fault so am assuming that the command to inject isn't making it to the injector.

My question is, where do I go from here and what needs replacing?

Cheers.