Update time:
I hand delivered a simple letter to BMW finance offices on Friday Morning.
I called them this morning and they tried to make me sign a load of documents. I told then that my letter is sufficient and I would not be filling anything else until collection.
They put me on hold for a while then came back saying I can arrange collection from anytime after midday tomorrow
They also have agreed that I am allowed to pay back the 50% balance which works out as about £1000 on a "payment plan".
They initially argued if I didn't pay them they whole amount upfront I would be defaulting, but I am perfectly entitled to pay the debt under pre-agreed installments and it has no affect on my credit rating.
I think I might just pay it upfront, but not everyone is in this position, so I thought I would see what other options there are and spread the word
It is possible to hand the car back early and re-pay the balance to reach the 50% number under a separate agreement.
I can see why the companies do not want this to be well known, but it is actually very easy when you know your rights!