Unless you have notified the DVLA that your vehicle is being kept off the road by means of a Statutory off Road Notice (SORN), you are not exempt from having to insure your car.
In line with Continuous Insurance Enforcement (CIE), it is now a legal requirement for the registered keeper of a vehicle to insure it even if it is not being used and/or is parked on private land. The only exemption to this is if it has a SORN.
Please see the websites in Related Information.