That's why I referred to 'badged policies' provided by CAMH, John Lewis, M&S, HSBC etc. Aviva appear to have the majority of the 'badged market', and they have replied to me with the latest version of their Cover Restrictions as I posted in Post #22 above. My policy renewal was 3rd February 2023; I don't recall being advised of the restriction on Cover, but I didn't read the policy booklet from Cover to Cover either. A request to extend the Unoccupancy to 90 days would be a variation to the Policy Terms, and therefore an amendment to the underlying contract.
Either way, Aviva will not play ball, and, unless you want to go through the tortuous and lengthy process of involving the Financial Services Ombudsman, with no guarantee that the ruling will be in your favour, the only option is to find an alternative Insurer. I need Legal Expenses Cover anyway and Aviva specifically rule out adding this cover mid-term
Steve