The distance selling regs with cars in the UK have always been a bit funny. Basically yes, they apply, and yes, you can test the car once you receive it, but put anything more than a dozen miles on it and dealers will argue(sucessfully!) that the car no longer fulfils the "must be in the same condition you received it in" criteria. Also distance selling regs don't apply to custom items, so if yours was built to order, you don't get that at all.
Basically with Cazoo you get 7 days, but also a certain mileage, and they won't ask any questions within that time or distance, they will just accept the return. You could probably try forcing them to take the car back within 14 days based on the distance selling regs, but if you've driven the car at all, in my experience you're going to have a really tough time doing so.
Built to order is not the same as a custom item. You'd probably need to pick a full, specific set of options for it to perhaps be custom. Just picking a colour out of a short list provided to you probably isn't a custom-made order. But yes, many companies try to claim that made to order means no return rights.
Anyway, it seems to me that Cazoo is not abiding by the regs with their 7 day policy [1], which additionally exposes them to more honerous consequences (because it's misleading and not telling customers that they have a 14 day legal period to return goods gives customers 12 months to cancel)
Basically with Cazoo you get 7 days, but also a certain mileage, and they won't ask any questions within that time or distance, they will just accept the return. You could probably try forcing them to take the car back within 14 days based on the distance selling regs, but if you've driven the car at all, in my experience you're going to have a really tough time doing so.