PFR don't take it lying down. Get copies of the local met report wind and rain gauge data. Compare rainfall intensity and wind compared to other storm events. Try citizens advice for any help they may be able to offer If your insurer hasn't resolved your complaint within eight weeks, or has rejected it, you can take it to the Financial Ombudsman Service . FOS has the power to award up to £150,000 against an insurance company. Claim forms can be downloaded from the FOS website or you can call 0300 123 9123. Give them hell! Some of the records are online others you may need to contact the met office(no idea of costings but would be nice to throw it at the insurance company to pay.)
I had a vaguely related problem concerning porkies being told about flood risk for a property. However gauges existed on the river with online records back to 1970. Having witnessed 2 flood events it was a very straight forward exercise to calibrate the records against witnessed events and extract similar events back over time. In your case you would be looking to demonstrate uniqueness of a weather event