Of which 50% are deliberate, and there is no breakdown of how many of the rest are random mechanical failure as opposed to having been involved in a collision with an associated fire.
Sorry, you meant 300 non-teslas will burn spontaneously, not as result of a crash or other emergency? Is that true? Seems to be incredibly high number.
From a quick search, Teslas make up about 1/1,000 of the cars in the UK (30,000 out of 30 million, very roughly). If Teslas burned at the same rate as the average we’d expect to see one Tesla fire every 3 days or so. (Of course there are lots of reasons that wouldn’t be true, like a huge amount of fires coming as the aftermath of thefts, and Teslas are harder to steal than average.)