Empty threats, say Brexiters of the claims made by Airbus and Siemens that plans are under way across industry to slash investment budgets and possibly close factories should the UK quit the European Union’s single market and customs union on 29 March. Worse than that, Mark Francois MP, an arch Tory Brexit campaigner, says it amounts to bullying. He said Airbus’s German boss was guilty of “Teutonic arrogance”. Yet, without a deal – one that at least keeps the UK…