I voted for the hamster design (though I love Ladybella's design provided the ears are altered slightly to differentiate them from the eyes). However, I voted for the closed helmet, as after discussion with other people who use helmets (as I needed to know this for my own helmet for trackdays) the best idea - even for in car - is a closed style helmet. You can get ones which have the chin section lift up out of the way or close down to protect the whole face. I'll try to find an example later.
The reason behind this is that if you are in an accident and have an open face helmet, it's not going to protect your head from hitting the steering wheel. A closed face helmet with a clear visor/no visor will still allow you to see the persons eyes - which is usually enough to identify them.
Also, as said by a couple of you, we need a helmet size. To this end, I've searched the BBC site for the last hour looking for a phone number for a relevant person. My thinking was to call the Health and safety guys - seeing as they've had to use Helmets before, chances are very high they've got his size on file somewhere. Unfortunately I was unsuccessful, so I've just sent the question via the Top Gear section of the BBC site instead.
I have to head out for a seminar thing for Uni, but if anyone else is successful in finding a decent number to call, I'll give it a try tomorrow morning.
Cheers,
Max