.....classic car policies don't earn you a no claims discount.
The type of policy that you'd have if you insured a classic as a second (or third, fourth, etc) car don't, no, but if the car is your only
car, then Adrian Flux among others offer agreed valuations on old cars on policies that do accrue and take into account NCD.
Last policy I had on the Dolomite as an only car was with Peter James, no mileage limit, NCD taken into account & ongoing and agreed valuation all set in stone. It's probably not advisable to run an only car on a policy that assumes it works part time. My last policy where the old car was the only car cost £80ish for the unlimited mileage and, strangely enough, wouldn't have cost any less for 3000 miles. I realise that younger folk will pay more, but to give an idea of proportion, the daily modern now costs a shade under £117 p/a so old cars are still cheaper to insure even if you shop for mainstream insurance and that needn't mean that you'd lose the option to agree the value.
I appreciate that this may not solve the issue of classic policies' availability for younger drivers, but as long as you provide an agreed valuation and get that accepted in writing, then why restrict yourself to using a car only as an occasional plaything?