Whether or not the lad had permission to "test" the car (yeah, right, we know what you were really doing), if I were the owner of such a vehicle I would have stipulated that such "test" drives were not allowed anyway - everyone *knows* what will happen once a garage gets their hands on a nice car - they are, after all, car enthusiasts. How hard is it to say "If it needs to leave the shop for any reason, you need to call me first." - it could have been parked where it could be stolen, got into an accident, taken for a joyride, etc. I don't care about it for my £200 Mondeo, I would care about it for a £200K Ferrari. And yes, I don't think I've ever owned a car worth more than a new petrol cap for a Ferrari. There are reasons for that, but the primary reason is that your car is very easy for *other* people to break. Second would be petrol running costs. About 20 or 30th would be any sort of aesthetic consideration.
Additionally, I would have probably invested in a GPS tracking device for said car ( £100-ish for a basic model). Hell, I have something similar on my car and that's nearly 50% of the price I paid for it! Not only would it lower the ridiculously high insurance, it would allow recovery in the event of a theft (which you *CAN* get charged for by the police), and it would also let you keep an eye on said garage that they were doing what they promised (I would have mentioned the presence of such a device to them at the same time I told them not to "test" drive it). It would also, in this case, provide evidence for possible TWOC and/or speeding in this case, both of which would mean the garage would end up in court, bang-to-rights, paying not only the cost of the car but also out-of-pocket expenses and most probably any increase in insurance you accrue because of loss of no-claims, higher premiums etc.
Taking a car to a garage is a necessary process. Allowing them to "test-drive" it is not. You can do that for them, at no more risk than they can, and 99.999% of things can be checked without an actual test drive lasting more than parking it in the garage's attached car park. And in such a bloody expensive car, you should protect it. It's a high-value, sought-after, easily-moved machine worth more than my house - are you seriously telling me that you never *thought* of putting, say, a GPS tracker on it for less than the price of a new door handle for that car?
Hell, I don't let other people drive my car unless absolutely necessary, and yet the single most expensive component in it at any time is the GPS and then the fuel in the tank (£70 for over 500 miles at the moment, which is over 1/3rd the price I paid for the car). I treble the value of my car every time I put my laptop / Satnav / phone in it on my way home from work, but still I take precautions with who drives it, how they drive it, and keep an eye on them *when* they drive it.