Yep
Only difference this time is that I stopped at a petrol station after 5 minutes (after which it ran fine) rather than carry on driving for miles.
Bear in mind that, if it detects a misfire, it'll probably shut down the affected cylinder until the next restart.
Is it still cylinder 3 that's misfiring?
I will reiterate that I recently did a lunch hour job replacing 2 out of 3 of the coil packs in a mate's one because they were intermittently tripping a misfire code (and you really notice when you're down a pot on these)!
You swapped the injector before, IIRC? so if it hasn't moved it's probably the plug / coil pack or outside chance some dodgy wiring (it's French, after all), and if it has it's the injector.