I might be teaching grannies to suck eggs, so apologies if this is old news...
I just spoke to Ford Credit about my current policy with them. In the past I got stuck "Transferring credit agreements" between cars, so when I bought my fiesta, and then upgraded to the focus, I had to transfer my credit over to them - a bigger bill as you could well expect.
After speaking to FC, I found out that you can in fact just hand the keys back at any point After you have paid 50% of your credit agreement! so if you owe 6000, and you have paid 3500, you are happy to write to them and cancel the agreement, and as long as the car is in excellent condition (your local dealer can tell you what needs doing to make sure it is!) then you can literally hand the keys back and bye bye remaining finance!
I didnt know this, and hopefully this information may save just one person out there from ending up with a bigger bill than they actually need!
Any scuffs or mechanical damage needs to be made right, and if they take the car and do the repairs themselves, they send you the bill and you pay it, or if you get the car sorted out yourself for much less, then you can save a lot more money! they just check the car and say "this needs this, that needs that" and you either give them the keys, or sort it yourself until they can say "OK, wheres the keys?!"
This mistake has probably cost me an extra £3000 in credit transfers, so I hope its useful to someone out there!
p.s. if this has already been covered, I apologise, I got so excited and thought I had to post it