Declared modifications not covered by insurance

se2020

There is no question about the mods not being declared. 
There is the original email listing the mods being added along with the increase in policy cost and admin fee.
There is also a recent email confirming that although the mods were added to the policy and are "covered" they are not liable for the cost of replacement to these parts.

Reading through the terms and conditions it only states that they have to be informed of any mods, it does not actually say if, once they have been informed, these parts are then covered or not for damage (or indeed if the van got stolen)

The latest correspondence says that the claim is being delt with in line with policy.
They pay out based on the fully comprehensive policy in place (not paying for the mods) and then they will claim from the other driver and, if that claim is successful (they are claiming from themselves!) the no-claims discount etc. will be reinstated.

Ectophile

In that case, it sounds like the only option is the Letter Before Action to the van driver (or their employer).  Tell them that if they don't pay for the hard top within 14 days, then they will be subject to court action without any further notice.

If they have any sense, they will pass it on to their insurer, who is liable to pay it.

rs65

se2020 said:

Reading through the terms and conditions it only states that they have to be informed of any mods, it does not actually say if, once they have been informed, these parts are then covered or not for damage (or indeed if the van got stolen)

You need to look at the definition of vehicle and also how they settle claims
Which insurer?