It is possible to get one insurance policy that covers several vehicles. Insurers that offer this service will generally give you a discount for each additional vehicle you add (usually up to five vehicles), so this would seem an ideal solution here.

The downside is that because this isn't offered by all insurers, you generally can't use price comparison websites to get lots of quotes at once - you'll have to go old-school and do some ringing around. Google will help you find insurers that offer this service, but as a starting point you can try Admiral, Aviva, Endsleigh and Liverpool Victoria. It may also be worth calling up your current insurer and asking if it's something they can help with.