Ah ha! Seems like the SV's didn't do too well on the way back from Donnington then! I had exactly the same problem and just popped on to see if anyone else had struggled...
Made it back to Manchester, but the A34 near Manchester's not the best fun around wet roundabouts when your two up with luggage and the engine keeps swapping between half and full power! Still have to say, those Metzeller z6's are great in the wet when your engine can't make it's mind up!
Just been outside to mine and it's still not happy, front pot comes in above 5k rpm, but it's a sh*t to start and people must think that you are a right nugget at lights keeping the revs up to keep it going!
Mine (SV650Sk3, just over 10k miles) has never had this problem before despite being ridden through winter, etc. but the plugs were changed on the last service and I can't help but think that they weren't done very well last time.
Just wondering, do you chaps have to take the radiator off to get to the front plugs as there's only about an inch of room to work with!
Still, next time it's going to be a 4 cylinder bike, just for resiliance!
