Its how you ask
I got a quote from Devitt for about £400 (fulL comp. new GS, not ridden for a few years).
Then dealer suggested I phone BMW insurance and found myself talking to Devitt again. This time they quoted £172.
When I queried the difference I was told they are only allowed to offer BMW insurance scheme when customer specifically asks for it.
So it seems the price depends on how you ask for the quote.
I was also told that earlier qoute was based on no alarm as BMW one is not Thatcham approved but with BMW insurance the BMW alarm saves about £20