Imagine being able to buy a Bugatti Chiron in 40 years’ time for £3.2 million. Or a McLaren F1 for £960,000. These cars are or have been the most expensive models on the planet, but it’s hard to see their values tumbling - in real terms  - to just 60% more than their original list price by 2058, unless we’re banned from driving petrol-powered cars altogether.