Well you could either cancel your policy completely if you are getting rid of the car. Or you could have them suspend the cover and hold fire and theft only cover on the car. But you wouldnt get any money back until you re-instated the policy.
if the car is parked on a public road or outside your house in a housing estaet, it needs insurance iirc.
also if it is in your garden and somehow goes on fire and damages your house or the neighbours house, you'll need insurance too.
if it was me, i'd put it in the garden and maybe cover with a car cover or similar just to protect it. theres also some fuel additives that you can put in the tank to stop the petrol drying up or something and it protects the fuel lines etc.
maybe disconnect the battery too.
from another forum -
The only fuel additive I use is a fuel stabilizer which I add to my M3 when putting into storage as it prevents the fuel going off and corrosion in the fuel lines etc I did not use it one year and the fuel in the car was crap but last year no problems.