Had 14 plate van so still in warranty. During recent hot weather had a/c on almost constant. Driving one day had smoke enter driver compartment from pass footwell. Managed to pull over before it burst into flames ! Subsequent (insurers) engr report says cause inconclusive as damage too extensive. Been offered bottom book but only done 20k. Any ideas / suggestions please

Find evidence that your vehicle is worth more, find similar vans for sale to show what it's worth.

Ask to be shown where they have found comparable vehicle close enough for you to view in the same color.
You were lucky they could not find cause