Hi Dan/Paul,
Most classic policies within the Insurance market do not accrue or require NCB, so you have to bear in mind that unless the NCB that you have earned to date on mainstream private car policies is being used upon another vehicle - it will not be taken into account (due to expiry) if you attempt to use 2 years after expiry of your last mainstream private car policy.
They do represent good value if you have a vehicle that is 20 years old, which is a 2nd non-everyday car that is recognised as a 'classic model' and on a low mileage basis.
The classic policies that we have access to are aimed at the non-modified original specification models such as MGB's, Triumph Spitfire's, E-Type Jaguar's etc.
If this expands to include a retro/custom capacity in the future (ie. to include modified vehicles), I will post on here to let you all know.
Kind regards
Tony