The Aviva Policy booklet States that “Theft of cycles (including Ebikes) from the garden unless securely locked to an object that cannot be moved” is not covered.
When I renewed last year I queried this and asked about garages and outbuildings and was told as long as the building is secure then the bikes do not need to be locked to anything.
I was on the phone with Aviva, the agent needed to check with underwriting about covering this specific bike to the value requested, came back saying yes but you need to do this, essentially an extra condition for cover, I abide by it and hope to never need to use my insurance.
My other bikes which are under the limit to be declared fall under the standard terms from the policy booklet.