2008 C-Max 1.6 TDCi ZETEC - "NO IMMOBILISER ID"....

2008 C-Max 1.6 TDCi ZETEC - "NO IMMOBILISER ID"....

I have a 2008 Ford C-Max 1.6 TDCi Zetec which up until last week was running like a charm.  However, on a couple of occasions during short journeys to and from school a warning tone sounded and a message came up "Acceleration Reduced".  This cleared within a second or so of coming on and the car continued to run as normal.  Until the end of last week when it just completely conked out.  I arranged for a friend to tow me to the garage and whilst en-route the warning cleared, turned the key and it all started up again.  Drove the rest of the way to the garage, but just as I was pulling into the forecourt, the engine continued to run but acceleration totally disappeared.  Was fortunate I could just roll it in.  Anyway, they hooked it up and it showed a load a fault codes were found and cleared but there is now just one - something along the lines of "No Immobiliser ID".  Now it won't start at all.  I've been told that it needs to go to Ford, which is fine, but I'd like to get a steer on what's likely to be wrong  before I throw a load of money at it if anyone can help out!!?  What could be wrong and how much of a bill am I likely to be looking at - bearing in mind the car is only worth about £800!