i was getting quotes of ~£400 fully comp but as the truck started to get modded i thought id better start declaring them - most companies wouldnt offer cover
so took the advice and went to frank p, they told me up front i'd need at least 5 mods or some some substantial ones if less in number - reason being that people who modify their car tend to look after them more and maintain them better which is why quote is cheaper - same on classic car insurances i have had over the years, stick an agreed value on and watch the premium go down - they know you wont wreck your vehicle! i had £15k cover on a vw bus for £99 fully comp limited to 8k mileage and they were right a was always too scared to drive or leave it anywhere
only spanner in the works is that the quotes of around £100 mark were for 2nd car only - again expected that you dont use everyday and only for fun/pleasure and so no cover for commuting regardless of agreed mileage levels. as my truck is main vehicle for me they offered same terms (green laning etc) but with commuting - cost went up to £250 but still good value. only downside is no NCD can be built up so you'd probably need to stay on this type of policy going forward - mind you my old insurer told me the NCD built up would "hold " for 2yrs.
in summary (i think) if you have no or limited mods go for a normal policy - even if ~£500. if you have mods they must be declared so go for a specialist and accept the trade off with NCD but gain on price and even better if not your main car.