I think you should check Top Gear ratings worldwide. It gets around 350million viewers worldwide so I think they can live quite well without Tesla.
A positive review on Top Gear on the other hand would at least have some effect on Tesla. Top Gear could live extremely well without Tesla. If Tesla succeeds and dominate the world in a few years then it would of course be another story.
Personally I love Top Gear and laughed a lot when they tested the roadster. If you dont watch the show regularly you might think its a car program. But it isnt. Its a program made by guys who happen to like cars
I expected the Tesla review to be just like it was. If you know these guys views on EVs then you cant possibly be surprised. If you want unbiased and thourough consumer advice on cars then you are better of watching another show.
I would never base any purchasing decision on a car solely based on a Top Gear review.
If they want to test the Tesla Model S they will. Several cars have been borrowed or purchased over the years to be tested on that show when the manufacturer didnt want to lend them a car for some reason. So Tesla can refuse, but mr.Clarkson will get a hold of one if he feels like it. Its as easy as that.