it's like meglet says: something made you lose control, whether it was a wet patch or whatever; losing control means... well, you weren't in control, and you have to be. Even if the witnesses agree you were doing 10mph, it was still fast enough for something to go wrong. If you can prove the piece of string in your engine broke suddenly, or a comet hit you from behind, you might have a defence; but other than that it's just you and a car that wasn't properly under your control. I don't really think you'll get out of this one, sorry.