An internal water valve starting leaking sometime between 5th December (when the Insured went on holiday) and the 14th December, when they returned and found the resultant damage to ceilings, carpets etc, some of which already had mould on them.
So max 10 days for the leak - the insurer is classing that as gradual damage and relying on that exclusion to decline the claim in its entirety.
Is there case law on what constitutes gradual damage?
To the layperson 10 days seems an incredibly harsh interpretation of the exclusion.
CROSSLEY GATES ANSWERS:
As far as I am aware, there is no case law on the interpretation of the words 'gradual damage' in an insurance policy.
However, the law relating to contract interpretation applies and that law says that interpreting words not specially defined in the policy starts with giving them their ordinary dictionary meaning. The dictionary defines 'gradual' as:
taking place, changing, moving, etc., by small degrees or little by little: gradual improvement in health.
I suggest the damage that occurs over 10 days is relatively quick damage and hasn't happened little by little. The speed of its spread may vary from item to item, but some of it (e.g. wetting of GIB board) may have happened quite quickly.