Given by LEGO (the company) to Hammond after he mentioned it helped him to recover.
It's not been made into a set though, as nice as that would be. I guess Top Gear is a UK only thing and I believe LEGO tends to think world wide for it's sets.
edit - and beyond the characters, and maybe the studio (which isn't that fascinating in terms of how to build it in lego), what else could be in the range? All the cars would have to be licensed by the manufacturers, not Top Gear...