Hi Phil,
sorry to hear about your problems, I have just got mine back from the dealers once again. This time they replaced the igniter. I had already replaced two coils as thats what was diagnosed by the RAC (Breakdown and recovery people) the first time it started missing.
This is my third igniter and the bike is only just 3 years old, I was lucky enough to have it replaced by Triumph at the dealership.
Hopefully this will be the end of it and it should run perfectly now

Hope you get yours sorted out, nothing worse than not feeling comfortable on your bike if you are travelling a distance of any kind..