From a financial point of view. This is how my CTR GT ended up being funded.
£4,900 loan left on my existing car, which was also the book trade-in value. They gave me £2,400 on top of that (so they basically gave me £7,200 for the car).
£2,500 down payment from my own pocket.
Total was worked out as £4,900 paid down on the car (ie my contribution, and the excess they valued my car).
Total to be financed was £10,000. Meaning the discounted OTR price for the car ended up being £14,900.
The £10,000 I 'owe' was then financed over 3 years on their Assurance scheme, and I end up paying £213 pm, and a balloon payment at the end if I want to keep it (although with the low mileage I do, the extra value will go on the next car I get in all likelihood).