Give me a car to drive and usually within five minutes I’ll have a sneaking suspicion about whether I’m going to like it. This will bloom into a fairly firm conviction within the hour and by the end of the day I’ll know.

I mention this only because I was so surprised by day one in Mercedes-Benz’s new B-class that I doubted my own judgment. So after dinner at the launch I sidestepped the bar and headed for bed early and sober.

But the next day confirmed what I had thought the day before: this is the least convincing product to wear the three-pointed Mercedes star that I can recall testing.

Mercedes calls this car a “compact sports tourer”. But given that it’s longer than a VW Golf, is utterly unsporting and, thanks to its disappointing performance, is a very compromised tourer, this proves about as convincing a slogan as the White Star Line describing the Titanic as unsinkable.

What is plain to see is that it is a mid-sized MPV, although you’re more likely to find the word socialist in a Labour party manifesto than hear anyone from Mercedes describe it as such.

I could forgive that and file it in the bin marked “marketing nonsense” were it not for the fact that it’s not even a very good mid-sized MPV. Yes, it’s undeniably spacious in the back and boot, but the interior lacks almost all the versatility for which the best cars in this class have made their name.

It has just five seats, the rear ones neither slide nor recline, and if you want to remove the seats (including that for the front passenger) you may have to pay extra, although Mercedes will finalise the UK specification only nearer the September sale date. The cheapest original A-class launched seven years ago had rear seats that slid, reclined and removed as standard.

When pushed, Mercedes described the Ford Focus C-Max and Renault Scénic as rivals, but these are cars with ranges that start at about £13,500 while Mercedes indicates the most meagrely specified 1.5 litre B150 is likely to retail at just under £18,000, for which money both Ford and Renault will provide 2 litre engines and a ritzy level of equipment.

A similarly specified B-class is likely to cost the thick end of £25,000, while if you chose the top-of-the-range B200 Turbo and equipped it with the leather upholstery, sat nav and panoramic sunroof Mercedes fitted to its launch cars, you’d be confronted with a £30,000 bill.

Other cheaper rivals include the six-seat Honda FR-V and the Vauxhall Zafira and forthcoming Mazda5, both with seven seats.

When the B-class does arrive here there will be four petrol engines — a 1.5, 1.7, 2 and 2 Turbo — plus 1.8 and 2 litre turbo diesels. But despite the fact that Mercedes says the entry-level 1.5 litre car will be the bestseller in the UK, not one could be found at its launch. Nor were there any other sub 2 litre variants to sample, petrol or diesel.

My experience, therefore, was restricted to the three 2 litre cars, the B200, B200 Turbo and diesel powered B200 CDI, and sadly, despite their position at the top of the B-class range, none rises above the mediocre on the open road.

Part of the problem is the electric power steering which, if you’re driving fast, makes the car difficult to place and little fun; at least the ride quality was commendable in all versions I tried. The engines are rather harsh when revved and the high central armrest meant I could not manoeuvre my arm into its natural gearchanging position.

Each version has merit: the Turbo is impressively free from lag and offers quite strong performance, the standard B200 is probably the best mannered of the trio, while the diesel at least comes with the promise of 50mpg fuel consumption. But in every case the Mercedes engine, which should be something to be savoured, is not.

It’s such a shame because the quality problems that have done so much damage to Mercedes’ reputation in the past few years appear much improved. Certainly the materials used in the cabin are in keeping with what you’d expect both from Mercedes and a car in this price range. In addition, those with large children or a small number of adults to transport will appreciate the capacious rear cabin and large, well-shaped boot. I also like the way it looks, which is not something I usually find myself saying about any MPV.

If only this car were as good as its clothes Mercedes might have been on to something. In fact what lies beneath that smart suit is overpriced, under-achieving and deeply disappointing.

It appears to be an attempt to use the Mercedes name and some slick marketing to dress up a rather underwhelming mid-sized MPV into something it is not and charge a fortune for it. I didn’t fall for it and nor, I suggest, should you.

Vital statistics

Model Mercedes-Benz B200 CDI
Engine type Four cylinders in line, 1991cc
Power/Torque 140bhp at 4200rpm/ 221 lb ft at 1600rpm
Transmission Six-speed manual
Fuel/CO2 50.4mpg
Performance 0-62mph, 9.6sec/ Top speed: 125mph
Price £24,000 approx
Verdict Costs too much, does too little
Rating 2/5

The opposition

Model Ford Focus C-Max 1.6TDCi Ghia £18,090
For Good looking, good to drive, interior quality
Against Only five seats, not as versatile as some

Model Honda FR-V 2.0 SE £15,705
For Six-seat system allows a child to sit up front
Against Too much wind noise, cheap looking interior