Assuming no deal and WTO, cars imported from EU countries will face the same tariffs as cars made in the rest of the world. British made cars will not giving them a cost advantage. Is it not possible that European manufacturers will look to set up production in the UK? Capitalism chases profits.
No, it makes no economic sense to makes cars in the UK just for the UK market – car makers require volume and so need to be able to export out of the UK and anything that makes that harder and more expensive is bad for the UK based makers.