Jamie, don't feel like a tart. I bet there's a few people this has happened to.
I had gone out in the morning on my 300. Everything was tickety-boo, then bosh....one cylinder and bugger all power.
Ah, that'll be a plug then, I thought. Pulled up at my mates shop, had a cuppa while waiting for things to cool down a tad, switched the plug, fired it up and hooned off. About 5 minutes later it was back on one cylinder.
Pulled the plug again, it was soaked, so I thought I'd just had bad luck and thrown in a dodgy plug. changed it again and zipped off. Good as gold for a couple of minutes then it's back on one again.
This time i wasn't going to just change the plug as it was obviously something else.
Thought I'd switch the coils to see if it'd kill the other cylinder, but as soon as I pulled the connectors off I saw that they were scortched and had been shorting. Snipped off the male connectors and fitted some new ones, cleaned up the coil connection with a bit of wet & dry and it hasn't done it since. Problem solved.