If you are thinking of buying a motor vehicle you could be considered crazy if you didn't at least have a test drive in a machine which was likely to be costing you thousands of pounds. If this vehicle is being sold by a large dealer they will probably have some motor trade insurance which could allow you to drive the vehicle legally; but do bear in mind that it is your responsibility to be absolutely certain that you are covered. If it transpired that you were not a court would not accept ignorance as a defence.
If you are buying from a small dealership or particularly a private individual it is still possible that you would be covered under an insurance policy that you held on another vehicle under a clause covering 'any vehicles not belonging to you or hired to you under a hire purchase agreement' or something like that. This would however almost certainly provide third-party only cover so if you were to bend a very expensive machine which still belonged to someone else you could have an difficult time trying to talk your way out of it. If however you did in fact decide to buy the vehicle the situation would change completely. You would now be it's owner which would mean that it would not be covered under that particular clause in your policy. So, although it would be perfectly legal for you to drive the vehicle whilst you were testing it, it would be illegal for you to drive it home without first taking out insurance cover to do so.
A lot of car dealers will try to sell you a full 12 months car insurance policy. Naturally they will get some commission from this and although they will no doubt offer you a good deal (as car dealers always do of course) you would be likely to get a much better one if you were sat at home, nice and comfy, in front of your computer. How do you get round this?
Simple. You can buy a single day's car insurance by visiting this website from your smart phone, Kindle, iPad or whatever. Within just a few minutes you could arrange comprehensive cover for a full 24 hours which would give you more than enough time to test drive the car, and then drive it home, secure in the knowledge that you were not likely to suffer the embarrassment of having to pay for repairs to a car dealer's vehicle out of your own pocket, or the even greater embarrassment of facing a charge of driving without insurance and having your new vehicle towed off to a police pound if you were unlucky enough to be stopped in what would, after all, be an unfamiliar vehicle.