I doubt the BBC's legal team would have allowed it to broadcast if they didn't think it would end up in their favour. The losers in this are the British public, who are presumably paying to defend the broadcaster from some car manufacturer who didn't like a review.
At least we have Loser Pays, so it feels unlikely that the license fee payer will actually lose out.
As Top Gear is a big winner for BBC Worldwide (commercial, not-license fee funded), it's been frequently the case in the past that they will fund any legal action should that become necessary.
True, but if Worldwide end up paying/losing, that means less money paid back to the corporation, therefore a lower budget for other productions (effectively the same thing).
I'm a fan of electric cars, but I am disappointed by Tesla on this... using the legal system like this leaves a bad taste.