Sometime in the future BMW will do what most people expect of a hybrid. It'll team its forthcoming super-economical three-cylinder petrol engine to its electrified transmission, and build a three-series that will do a month's round-the-clock urban jamming on an eggcup of petrol.
But right now, it's doing the opposite with its hybrid. It's using a 306bhp straight-six turbo with that electrified transmission, to make a car that'll do 0-60 in five seconds.
That's the thing with hybrids. They're not about economy per se. They're about efficiency. The electric system recuperates wasted energy from momentum and from occasions when the petrol engine has energy to spare. That energy is stored in the battery, and spent via the electric motor.
You can choose to spend that saved energy in different ways. You can use it on replacing engine power, to use less fuel. Or on augmenting the engine power, to go faster on the same fuel.
In theory, the BMW ActiveHybrid 3 can do both. Yes, in theory any hybrid can. If you cane a Prius, it goes faster than you'd expect for its 98bhp petrol prime mover. It's just that you don't flog a Prius because it hates it. Whereas the ActiveHybrid 3 adores being thrashed.
If you go gently, the ActiveHybrid 3 is a fair bit more economical than a 335i. But going gently is not in its nature, and if you go flat out it's even quicker than the 335i whose petrol engine it shares.
The result is a rather strange car. I did manage, for a buttock-clenchingly frustrating few miles, to drive in such a restrained way that I matched the official economy of almost 50mpg. Maybe it wouldn't be so frustrating if you had a traffic-choked daily commute. You could make a game of seeing how high you could stretch the economy graph.
But when the chance to use more power presents itself, this car is an irresistible temptation. When I got to some open roads in the countryside, I hit ‘sport' mode on the central rocker switch. That way the consumption was worse than 20mpg.
See, it doesn't drive like a hybrid. It uses the same system as in the ActiveHybrid 5. There's no strange CVT. Instead the electric motor is integrated into a normal eight-speed autobox. When the petrol engine is operating everything feels normal. But sometimes, if you look at the rev counter, you'll see the engine isn't working: it gets smoothly decoupled and turned off so the electric motor can gently move you. Away from rest, if you tiptoe the pedal, you can sometimes get to nearly 40mph on e-power alone.
Really though it's a huge amount of engineering effort and cost for a fuel saving that's noticeable only in slow town driving.
The performance gain is nice, but it isn't all that great: the petrol engine is 306bhp, the electric one takes the total to 340bhp. Which is only really like going from a 335i to a notional 337i.
And it costs an extra £5695 over the 335i. It makes sense in America and Japan where no-one drives diesel cars. But in the UK, unless you have a very particular company car tax situation, tread carefully.