I experienced bad behaviour on all my carbed bikes, even after 2 months of storage. My lawnmowers and other household gas-powered appliances were even worse, no idle, etc. (manufacturers recommend draining the fuel if you don't use the mower for a couple of weeks - maybe they're onto something). Disassembled the carbs multiple times, there were greenish residue in them, cleaned with ultrasonic cleaner. Most of the brass parts (jets and others) looked heavily eroded under magnifier. This was on normal E95 with 5% ethanol only, now the standard is 10% ethanol. Since I realized all these problems were caused by the ethanol, I changed to 100 octane premium gas with MTBE (?) additive instead ethanol, and my problems are disappeared. I don't live in the UK, for your reference. However the Fazer has the eroded brass parts in it, somewhere in the future I have to replace everything, ouch. It runs OK after carb sync, but it's bugging me...
A small amount of 2 stroke oil can be mixed in when filling up with gas, it helps to coat and lubricate the parts of the fuel system, useful in winter storage.
Regarding "nobody has starting problems on ethanol fuel" well, I guess the 4 cylinder bikes are forgiving, they run even if there are small problems. Try to kickstart my TT600R thumper with ethanol ruined carb... that's a different story.