I've cancelled an insurance policy once and started a new one when buying a new car, only because I couldn't get covered on the car I was buying. Took quite a hit to cancel it mid term as they take quite a hefty cancellation fee. Your best bet would be to phone your insurer, tell them you are thinking of changing cars and see how much it will raise your premium by. Also ask them how much it will cost you to cancel. Don't forget you will also be starting this years of no claims discount build up again, if you are not at full already.