The crankshaft of the BMW Mini, which is the bit which transmits the power of the engine to the wheels, crosses the English Channel three times while the car is being made. It is cast in France; it goes to a plant in Warwickshire to be milled and finished. It is then shipped to BMW’s plant in Germany where the engine is assembled and comes back as part of that whole unit to be fitted into the car at the BMW plant near Oxford. When it is exported to Europe, as very many of these cars are, it crosses the Channel for a fourth time.
This is the reality of modern sophisticated manufacturing. Three channel crossings is actually quite modest for a component. Some go back and forth much more.
You could tell a similar story about Bentley, Jaguar Land Rover or about the wings of the Airbus aircraft which are made here (though the plane as a whole is assembled in Toulouse) about much of the output of Rolls-Royce or BAE Systems, the pillar of the UK defence industry.
We don’t have nearly enough world-class manufacturing to support our exports, but what we do have is heavily dependent on key components from the rest of the European Union. This business arrangement becomes totally uneconomic if we do not continue to have free trade but instead had to pay the common EU tariff of 10%. Most of the components industry operates on a profit margin of between 5% and 10% so it would become unprofitable overnight.
And if a supplier upped prices to compensate for the tariff it would be uncompetitive. There would also be a huge additional cost in time and paperwork because the component would be subject to customs checks each time it crossed the border.