couldn't wait till monday, went in today and scoped the injectors. no.1 was drawing approx .3amp more than the rest so swapped with no.2, missfire promptly moved to no.2. new injector not available today so treated with forte specialist injector cleaner and left running for half an hour.running has certainly improved and emissions are back to normal, but i think i will still replace the injector on monday to be safe. thanks to all for help, dave.