Tesla sales slumped 40% across Europe in July compared with a year earlier as Elon Musk’s electric car company faces increasingly tough competition from its Chinese rival BYD. There were 8,837 sales of Tesla cars last month across the EU, the European Free Trade Association and the UK, according to figures from the European Automobile Manufacturers’ Association (ACEA). That compared with 14,769 at the same point last year. New car registrations for BYD across Europe rose to 13,503 last month, compared with 4,151 a year earlier. BYD now has 1.2%…