I have found in the past couple of years that the most competitive quotes for classic car insurance is from Campbell Autoline, details below:
Campbell Autoline,
38 Railway Road,
Coleraine,
BT52 1PE.
Tel: 02870 345885.
I have the 4 cars on one policy with them, and no other company could even come close on price.
Worth a call when your insurance is due for renewal.