Charging higher premiums for mods and actually covering mods in the insurance are separate things.
Premiums are largely calculated from the statistical likelihood of you having an accident or your car blowing up or getting stolen. All the questions they ask about the type of car, mods, parking location, milage, etc. are all just to help calculate the odds of you having an accident. The actual value of the car and the mods has little bearing on your premium.
I think you'll find that modified cars are statistically more likely
to end up incurring insurance claims - and it doesn't matter whether the insurance company pays out to cover the mods or not, they'll still be out of pocket, so they'll still look to charge you more on your premiums.
Sorry to hear about the car bridlea - I don't think Elephant cover mods OR do agreed value? In which case you can probably expect a big argument.