Yes I think we all established Q made a number of mistakes here (and driving her back to the station was stupid) but (from what I can remember of the op) short of Q getting violent she wasn't going to let go of the £300.
Anyway, I think this thread shows that there are good lessons to be learned.
Agreed - as I've said a number of times. I'm quite prepared to be shot down for being a nice guy vs being a total bastard - as Akauya and others have said, not sure what else I could have done differently without getting physical with her.
After 30 mins as I said I asked her plainly to "move things along" - she then sat on the sofa next to me but still kept talking machine-gun style. This is clearly a time-wasting tactic she's mastered and not something that just casually happened. No doubt a more hardened punter would have confronted her - resulting in her walking with the money anyway - unless he were prepared to get physical with her. For all I know she's done this before and when a punter does try to get physical she cries rape or threatens to do so. She is a twat but a wily twat. If you're so confident you wouldn't fall for that crap - book her yourself and see how you get on. Look forward to the review.
As for taking her back to the station - as I said before I could have cut my losses and just kicked her out the door and told her to find herself a taxi but I was still trying to convince her to give me my cash back and still taking the view that being nice had more chance of getting my cash back than being a bastard which would have ended that discussion there and then. No, it did not get my cash back but what did it cost me? Nothing. And as a result I know I tried everything possible to get my cash back, and I 100% fulfilled my end of our agreement which was to pick her up from the station pay her for the activities we agreed in my booking, and then drop her back to the station again.
Not necessarily a great consolation, but at the end of the day as I said elsewhere I only punt with money I can afford to lose. Financially I'm no worse off as a result of this than I would have been had I fucked her senseless for 2 hours. Just with slightly bluer balls and a bit wiser.

Lesson learnt - I will be limiting my exposure to high risk meets like this for the foreseeable future although I don't 100% rule out a similar meet as I know that would exclude me from finding the occasional "outcall only" gem like Mitzi Maraschino - my TOFTT of the year.
In future the only way I will see an unkown / unrated (on UKP) outcall only girl is by rb however - as at least then I am getting a much better rate which significantly reduces my exposure - I will also be much more wary and be looking out for some of the alarm bells Ben pointed out in Becky SummerPsycho's profile.