Once upon a time, the C-Class was the ‘baby Benz’, the easy-to-park runt of the Merc litter. But with the A-Class - not to mention B-Class, CLA and upcoming GLA crossover - sneaking below the C in the smallness stakes, Merc has sent its 3-Series rival upmarket with this all-new generation: more space, more lux, more tech.

So the C-Class has swollen in size - by 10cm in length and 4cm in width, no less - with a chunk more room for bodies and boot-items. It’s bigger, but not heavier: thanks to liberal use of aluminium in the body, weight is down by up to 100kg.

Which means more metres for your litre (of fuel, innit). The fourth-gen C will launch with two sensible petrol engines - the 154bhp C180 and 182bhp C200 - and the 168bhp C220 diesel, which officially returns 71mpg and just 104g/km of CO2. But there are yet-greener variants on the way: an upcoming 113bhp 1.6 diesel that Merc says will out-BMW BMW in the efficiency stakes. Down the line we’ll see a C300 diesel-electric hybrid, and, after that, a plug-in version. The launch engines get a six-speed manual as standard, with the option of Merc’s seven-speed auto.

Talking of auto, the C nicks much of the new S-Class’s ‘intelligent driving’ tech, scanning for danger ahead and braking autonomously from 125mph. Check the right options boxes and, at speeds under 37mph, your C-Class will follow the car in front at a safe distance, even steering to keep you on the right course. That’s sophisticated stuff from a car that should start under £30,000 when it goes on sale in the UK in spring 2014.

There’s an Audi-style touchpad that recognises all the swipe-pinch-tap gestures familiar from your smartphone. Spec Merc’s under-lettered COMAND nav system and you get an 8.4-inch central display screen. That nav, incidentally, chats to the C-Class’s air-con unit to inform it when you’re in a tunnel, engage its recirculation mode to save you breathing dirty tunnel-air: a very clever and very complicated way to solve a problem we never really knew existed.

We suspect you may wish to know about the uncomplicated stuff: the firebreathing AMG version. Well, there will be a hot, smoky C, but it won’t use the current C63’s vast, atmospheric 6.2-litre V8, instead a turbocharged unit likely a new bi-turbo V8 making at least 450bhp. That car will ask some mighty stiff questions of the BMW M3 and M4…