I don't mean to break this up but it would be nice if we could leave an argument in the topic it started. By all means debate with each other through pm and on the original topic but it's a bit unfair to the guy who is genuinely trying to find the price of his car.
To return to topic
Mate I had mine up for sale advertised at £20k
25k miles, Tornado Red, DSG, 17 inch, cruise control -that was it.
Had 5 people this week trying to buy it. But I had changed my mind and it was no longer for sale.
(Funny that... not a bite in the first week when I would have given it but as soon as I decided to keep it everyone phoned)
I think if you have less miles and a bit better spec then £21k plus is attainable. Give or take £500 if you want a quick sale/ better price but all in all you should safely get over £20k.
Oh and when I was considering trading it in every garage I went to was offering £18k (even VW garages) with the BMW garage offering £18,600. So unless you are really stuck don't trade in!