Ben Waine, what insurance company was that?
My advice to Matt is to flog the mini, use the capital to buy a car that is in the insurance category 1 as this is stupidly cheap to insure (relative to your quotes). For an example, Last year when I was 17, I insured a Chevy spark for £1600 which was before the ruling by the European Courts that it was sexist to charge males more than females. Thus you should find it even cheaper to insure. I used direct line, you have to phone them though. The good thing about cat 1 insurance cars are they seem to have a value depreciation plateau between around 20k miles and 50k miles, what i mean by this is they seem to hover at that a price and so if you only do 10k miles in the year driving to get your no claims, you won't lose much as it will resale close to what you pain - tis what I found anyway. Also newer cars are far less likely to go wrong so that avoids expensive repair bills. Plus cars like the chevy cost £26 to tax.
So drive a car like that for at least a year to get your experience up whilst gaining your NCB.
Now listen here, don't do what I did and sell the sensible car after 9 months and buy a car that, I quote my self, "don't mind scratching nor crashing" as I am now sat here, writing this with a broken back in three places and a broken neck. Having a more expensive newer car seems to make you more cautious and sensible which in your first year is very helpful.
So basically be boring for a year, save money and then upgrade to a landy when you're wise and its economical sensible because remember the money you pay in insurance goes in to a horrible abyss, so the more that gets swallowed, the more you'll kick yourself later...