"Being part of the single market is fundamental to the current strength we're enjoying," Mark Hawes, head of Britain's Society of Motor Manufacturers & Traders. While the drop in the pound since the June vote to leave the EU has helped car exports from Britain, overall uncertainties are casting a shadow over the future. Carmakers do not know how much production costs will rise, and whether the increases will end Britain's attractiveness as a platform for building cars and getting them into the European market. Several major British brands are owned by foreign companies — Vauxhall by U.S.