Bentley is one of the expensive car in the UK and the luxury outstanding and what is more, it's really affordable to buy a used one. The most important thing is to sell your other car first because you wouldn't be happy to be spending for 2 car if you don't need.
Just sell your car online by searching for car buyers or where can I sell my car http://www.cars-on-this-day.co.uk/category/motoring-tips/
Other places online to sell a car like Bentley:
1) www.bentleymotors.com 2) http://www.autoguide.com/new-cars/bentley/ 3) http://www.autoexpress.co.uk/bentley/flying-spur/87605/bentley-flying-spur-best-luxury-cars