Rich and Brian,
I don't know how this works in the UK, but where I live, insurers stick to the law, not to Home Office guidances, since these have no legal status whatsoever.
So unless your insurer makes specific provisions, either their own or referring to a document from a third party (which the HO guidance essentially is) in the contract, I would expect that you would still have the law on your side.
Is there anything in the relevant Act that distinguishes a rifle from a pistol? (I sure hope that the Act doesn't refer to the Guidance...).
The Filthy Pig
: Air Arms 100 (1990) + AA Olympic trigger + Welham reg + Custom Shop CS1000 stock. Status: leaking.
The Unknown Quantity
: AA EV2 Mk4. + BSA Platinum 10-50x60 + Jon Harris wheel. Status: sorted up to 25 yds.
The Limping Dog
: Air Arms Shamal (1989) + unknown origin sporter stock + Optisan Cobra 3-9x42. Status: slowly leaking; needs work.
: HW97k + Venom Lazaglide. Status: working just fine; needs scope.
with apologies to NJR100