When I got insurance last June, several companies didn't have the HS PHEV in their group listings and so couldn't quote. My insurance was with the AA and they, like some others above, wanted a cancellation fee. I complained that just because their underwriter was inefficient and hadn't got the HS PHEV listed it wasn't my fault because many other companies could quote OK. After a couple of days, they got back to say their underwriter had added the car and covered it for the year with no extra fee.
It would seem that still some companies haven't got it in their grouping systems, which is a bit weird.
To be sure though, every company I got a quote from classed it as 'MG motors UK' and not just MG.