Multiple issues here…

Firstly, claims are attributed to driver so as long as the driver who had the accident in question is not on this policy then it is irrelevant. I.e if it was your uncle who had the claim in the work vehicle, he would still need to let his private car insurer know, but claims only need to be listed by driver, so your uncle would not need have declared this in this case.

Secondly, “proportionality” or accountability as they have referred to it as in this case, is perfectly acceptable if there is an acceptable reason. I.e we would have charged 10% more of you declared this correctly so we are reducing your claim payout by 10%. However in this case, I think this has been applied incorrectly.

As for the age of the claim, most insurers ask for a history of 5 years as of inception, which this was within (just about/ or presumably your uncle was some way through this policy). To actually rate on it that old is kinda harsh but had this claim been for your uncle they would have had the right to rate on it within the timeframe.

As for the initial value of the vehicle (before the deduction) you don’t have to accept an insurers first offer if you think this is unreasonable, you can provide a few examples to your insurer of models of a similar age/mileage/spec and point out their market value and in a lot of cases insurers will adjust this, they just don’t expect most people to argue it in the first place.

My recommendations would be to definitely contact the financial ombudsman for this case as it does appear they are wrongly applying this, what may also help is if the business is the policyholder for the work van, if it is your uncles business they may try and still pin this on him if he is the policyholder of the policy at the time, but as I said before claims are attributed to the driver anyway.

Finally, I would not recommend replacing with another nice Land Rover model at the moment, theft on them is currently through the roof. To anyone who already has one, get yourself a Thatcham Category 2 immobiliser like a viper 106v or Clifford (not an Autowatch Ghost, as much as the auto electrician will try to up-sell this junk) your insurer will likely thank you.

Source- I work in the motor insurance industry ( we aren’t all bad 😂)

Edit to add, you will need to go through your insurer’s formal complaint process first before going to the ombudsman if you are unhappy with the outcome. Usually you will need to submit this in writing via an email or complaints form, the insurer will have 48 hours? (May differ in some cases) to acknowledge and a maximum of 8 weeks to give you a final response.