One of the most famous VAT cases everCake, the clue is in the name. They even baked a giant Jaffa cake in a court case to prove that they're cakes not biscuits. The difference is a cake goes firmer over time when exposed to air, while a biscuit gets softer (or you could say a cake goes hard and a biscuit goes soft and moist, if you want to go all "Carry On" about it, stop sniggering in the back there).
Still goes great with a cuppa though.

I have eliminated the first 10. Elimination based on my view they are ****e.