No matter how often you use your vehicle, unless it is officially declared off road by means of a Statutory Off Road Notification (SORN), it will need to be insured at all times.
If it is someone else’s vehicle that you want to use every now and then, then as long as they have an active insurance policy open, you can take out a temporary policy that will last from 1-28 days to cover you as and when you need it.
But beyond this, there is no escaping the need to keep your vehicle insured. Luckily, there are various steps you can take to make sure that you’re not paying any more than you need to in order to do so.