According to Musk, the ultimate aim is to be as big as BMW. "We'd like to exceed BMW volumes. The goal is to make a difference to CO2 emissions in the world. You can only make a difference if you can sell a lot of cars."

But can Tesla do that all by itself? Or would he consider licensing out the drivetrain to other manufacturers?

"We're certainly interested in licensing the battery, the drivetrain and so on to other car companies. We're already in fairly mature discussions. I can't tell you with whom, but they are some very large car companies."

All of which is good news, especially taking into account how the price of fuel is rising - particularly in the States. Musk points out another issue with petrol: "China has something like only 35 million cars on the road. They have a population of 1.3 billion.

"India's got a comparable population and a comparably modest number of cars on the road. The demand for gasoline is just going ballistic and we are not discovering lots of new, easy sources of gasoline.

"I think, just based on true demand, without any taxes being imposed, gasoline could easily hit $5 in the US in the next 20 years. Then it would cost you $100 to fill up a 20-gallon tank.

"Compare that to the cost of recharging your car to go the same distance [as a full tank would get you] which will be maybe $3 or $4. It doesn't matter whether you're environmentally aware or not, you will not buy the gasoline car."

So, petrol is not the future. But what about fuel cells? Others in the industry are pushing them as the future of motoring. Musk disagrees. "There really aren't a lot of alternatives to batteries. The use of fuel cells is flat-out stupid and anyone with a fair knowledge of physics should understand that.

"Fuel cells are not used in any of the most expensive phones or laptop computers. Even satellites which might cost $100m to build use lithium ion [Li-ion] batteries. Now surely you'd use the best option in a $100m satellite wouldn't you? There are also some basic energy equations that show that [using fuel cells] is quite stupid."

The only concern for those of us who've spent hundreds of pounds on batteries for our kids' toys is lifespan, then. But again Musk has an answer. "Historically, battery performance has improved by about eight per cent per year. I think it's reasonable to extrapolate that sort of improvement for some more years to come, driven primarily by the laptop and cell phone industry."