To be on the electoral roll, don't you have to be paying countil tax?
I had a devil of a time getting insurance when I moved back to the UK from Auckland (Devonport) in 2012 (I mention the year because so much 'my personal experience' becomes irrelevant within even a short space of time).
My NZ NCB was not accepted.
I did find insurance once I had a rental leasing agreement and a council tax account.
Seems to me that you are best to either be a named rider, as you are contemplating, or...,just rent a bike for the periods whilst you are going to be in the U.K. and retain flexibility over model, etc.and the insurance comes with the rental. You'll have no maintenance charges, no MOT. Plus, you'll have no 'sunk cost' in your capital being tied-up in a single machine that's depreciating in value.
You might only come out even over going your original ownership route plus paying council tax, but you'll have better cashflow and lump sum funds