This is excellent news...it sounds to me that you can have your deposit back - legally.
Having entered into a Three party agreement (you, garage and finance company) any party can withdraw from the agreement at any time up untill it's final execution. As part of this, you are entitled to your deposit back - less any reasonable costs incurred to the garage for having had the car 'off sale' in the interim.
Seeing as the likelihood of any costs being incurred is very slim, then I would expect the return, in full, of your deposit.
Tell the garage you know your rights, maybe even talk about trading standards - they'll most likely back down.
JJ
You gotta tie yourself to the mast my friend, and the storm will end.