Sorry Keith, forget it, you won't get enough to cover your finance. Ignore glasses etc. as in reality you are looking at 20 to 21k if you are lucky.
Just downgraded my Z4 sdrive20i auto and got £22k, Glasses said £24k+
Several BMW dealers were approached and the best I could get was £21k on a trade in for a 1 series, others wouldn't even give a price. BMW are still giving stupid discounts on new which are hammering residuals. The most annoying bit was my local dealer offered £19k! Oh and my car had lower mileage.
I was only able to get the £22k via a specialised small trader that buys a few niche cars at a time and he then only asked £22,950 for it so no huge mark up.
Oh and I am now in a Hyundai i20

but at least I should be in my nice new house next week