Most insurance policies are actually re-sold, ie, if you are insured through Tesco, they actually buy that policy from someone else, say from Fortis, they inturn have probably bought that policy from another company, and i have heard that over 90% of all insurance policies in the UK are ultimately covered by Lloyds of London. So, what i am trying to say is, yes you 'could' set up an insurance company, but you would still need to purchase a policy from an overwriter, you couldn't just make one up, and a single person buying one like that would either not be possible, or be very expensive. If you could do it cheaper and still legally then don't you think someone else would have done it already?
And as an aside, the average penalty for driving without insurance is approx £300 and 6 points, the average young persons insurance is approx £600, so why not just drive with no insurance? If you get caught you have just saved yourself £300, and the points wont matter as you don't have insurance, so the premium won't go up. Its a win win situtation. Obviously, the above is WRONG, ILLEGAL and i farking hate people that drive without insurance. So don't do it. Ever.