I hope Tesla can get as many to the UK before Brexit
You never know, we might get a trade deal with US and they will get cheaper....
Non EC Manufactured Cars - 10% import duty
EC you pay £50 flat fee
So after Brexit, when we are allowed to negotiate a different trade deal with US you could see a 5-10% price drop. Bear in mind that 20% VAT is also mandated by EU, so that could go down too.
It really will all depend on what UK Gov want to do after that. Certainly the price wont go up - even if the pound falls lower (it's already @ 1.21) it unlikely it'll drop to 1.1 or even 1.
Of course, none of that could happen, we could raise import tax even higher, who knows...
One thing is certain, German cars will get a bit more expensive.