I think Wessie mentioned some time ago that the main problem is the way insurance consider the risk individually Vs grouped, as this was explained in one some tv program about insurance, do I remember correctly?
You were answering to me saying that this insurance issue is almost non-existent in the EU (at least in Italy where I asked fellow 1300 owners).
As I said via MP and as I said in another thread, you are facing the same issues I faced for years before renting a lock-up to store the motorbikes.
And even the lock-up is now an issue.
Communal garages are "bad".
I used one that would be locked (with the guard inside) at 8PM. No way.
Insuring a GS anywhere in London is a problem. I face similar complexities insuring my 18 year old 1200GSA of a total declared value of 3k (against >1k premium). And it's still an issue even when trying to quote without fire & theft for some reason.
This is the same issue, on smaller scale, as Range Rovers & co.
If I try to insure my HP2, that is valued much more than 3k, on its own I don't have to jump through all those rings of fire required for the GS. And it costs 250 quid on its own (declared value >11k).
Again, I said it before. It's reaching a point where managing insurance is getting a bit ridiculous.
This can (my assumptions) be due to both rampant micro-criminality in London, for which the rather big increase in cost for a part of the population is apparently not an issue for the elected Mayor, and due to the the way motor insurance seems to work and manage/calculate risk.
I think this is something that could/should be covered a bit more by newspapers to try and push the relevant bodies to work towards a solution or improvement.
Small motorbikes (not GSs

) can and do help ease congestion and can be a transport alternative for some medium distance commuters. A lot are available on electric motors, so zero local emissions. Motorbikes and scooters also used to be classed as light vehicles (the ones pushed a lot into inner cities) until change of verbiage in recent years.
Sadly I do not see this happening as "defending" anything remotely related to "motorists" (electric or not) seems not to be kosher lately.
And I say this without wanting to get into into any conspiracy theory.
In your specific case, I think an UK dealer will be at loss of about 20 grand.