Hi Shukes:
Unfortunately, the fact that you drove on a public road is your downfall, regardless of it being a third of a mile or fifty miles. That's not my view, it's simply the law.
I sympathise that you were doing a mate a favour and if you get a summons to go to Court, I'd certainly at least mention that to the Magistrates. You never know, it might soften the blow a bit.
It might also help if your mate also went to confirm your story, not that it changes what happened but it sounds to me that it's the least he could do.
I can't see you being banned but points (at least 3, prob 6) and a fine (perhaps your mate could go halfs?).
Sorry I can't do better than that. Good luck.
P.S. Don't forget to go to the nick with the producer and take what docs it specifies, even your insurance certificate although it didn't cover you for your mate's car.