How much would the balloon be for you to keep the Mk6? I reckon it would be less than what you are likely to have to spend to 'own' a much older car.
Generally when lease cars go back, they are sent to auction where they will make trade price. That will be all that the lease company will expect to get. If you buy a second hand car from a dealer, you will be paying retail price. The difference between trade and retail on a £10k car will average around £2k. Also, you know the Mk6. If you buy an older car, you won't know where it's been or what it's done. That has to be worth something at least.
If you are insistent on getting dripped up to have a car, it makes little sense to line the dealers pockets, when you have your ideal car already on your drive.