@petra
How do you reckon the UK will be trading with the EU on our own terms?
Taking the example of German cars... The British are going to have to pay 10% more for German cars as a result of the devaluation of the pound, which most experts (yeah! I know! They know nothing!) don't think will recover.
It will then be up to the UK whether to impose import tariffs. It's the age-old story of whether to protect home-produced goods or whether to make imports cheaper to try and keep down inflation. The UK is going to have to go out of its way to protect Nissan with its 6,000 jobs and about 30,000 in the supply chain. Nissan is going to find it more expensive to export (and most of its production goes to the EU), so it can't afford the EU to impose tariffs. If they do, Nissan will transfer production to Spain (which would help the Spanish economy immensely).
Osborne has already announced a reduction in corporation tax to try and keep companies like Nissan in the UK, but that tax shortfall is going to have to be made up elsewhere, either by tax rises or spending cuts, both of which would cause there to be less money in the economy, possibly triggering another round of quantitative easing.
However, the negotiators and politicians decide to play it, the UK most certainly doesn't have the upper hand.