So what is the coolest car to drive in these conditions? Well obviously it needs air conditioning, or so you might think.
The obvious choice is a convertible, except that you really do need head gear otherwise heat stroke is a real possibility. I rather think that a French Foreign Legion hat with that neck flap arrangement, which kiddies wear, may be the answer. You will still be very hot, though.
Sunroofs have gone out of fashion a bit but they still have their place, in the roof. The panoramic ones are wonderful but you really need a re-gas of your air-con to ensure that you can survive that one. You may just be able to pull over a cover though, but know that there are all sorts of clever photochromic devices. You can also get fans in seats, but I am not sure if you can easily retro fit one from a salvage Mercedes S-class into your Vauxhall Cavalier.