Wreckered road test
First problem: to take full advantage of the Sea Class' amphibian features, you'll need a Certificate of Competent Crew from the Royal Yacht Association. This will allow you to drive around British coastal waters and up and down most inland waterways. Having done that, you'll find the lightweight coupe (aluminium wings, composite bootlid, thermoplastic wings) a joy to handle in the wet or the dry.

On the road
I took this astonishing amphibious car for a spin up the Thames. Needless to say, I turned a few heads as I roared past sedate old barges, working ferries and haughty old buffers in their river cruisers.

Still familiarising myself with the workings of the retractable rudder, I happened to ram a police launch at 30 knots and found myself being pursued by angry river cops . A high speed chase ensued with the Merc consistently outperforming two inflatable dinghies and the now sadly listing launch.

Just past London Bridge however, I hit a pod of porpoises and badly damaged the driver side wing. Fortunately there was no serious breach of the car's hull and the powerful new wipers were easily up to the task of removing bits of porpoise from the windscreen. Full marks Mercedes.

Heading west at speed towards Hampton Court Palace, the Merc's Hazard Control Software alerted me to a blockade of the river. The police had changed their tactics and radio'd ahead to colleagues who had scuttled half a dozen river cruisers in an attempt to halt this remarkable car. Well, call me a pig-headed old goat, but I like a challenge and so I simply put the foot down and aimed at a handy water ski ramp which was just visible in front of the sunken vessels.

The Merc's 4.4 litre V8 engine (combined with a high performance outboard motor) slammed me onto the ramp and I went sailing over the hapless police and their blockade. Unfortunately, I underestimated the power of the car and flew towards the riverbank and landed heavily on top of a horse which was pulling a barge towards Teddington Lock. Imagine the surprise of the barge's owner to see his faithful old horse crushed underneath an amphibious luxury car.

In the cabin
First things first - there is no cabin boy included in the cabin. Shame, that. However, the plush interior includes an iDrive controller for viewing non-essential functions (with optional HUD for satnav and speed projections).

Climate control and top end Linn hi-fi are standard features as are the emergency flares and inflatable escape podule which are tucked beneath the parcel shelf.

The onboard systems also include Active Cruise Control which slows the car automatically if another car or vessel pulls out in front and a handy fish-finder sonar display which will detect shoals at up to five fathoms.

Ride comfort is superb with multi link suspension and Adaptive Hovercraft Ballasting which keeps the car stable in even the choppiest seas.

Plenty of head and legroom in the back, proper wood and proper leather, good visibility throughout and while the seats may not be the zenith of sporty lateral support, nevertheless they are comfortable and heated and the driver's seat not only swivels 30 degrees but has curved armrests which give it the feel of an old fashioned "captain's chair".

Boot space is generous. I managed to pack in a set of golf clubs, a picnic hamper, a suitcase, fifteen breadfruits and a collection of exotic plants. The back seats fold down to provide a galley space for cooking and relaxing.

Overall, I can find little to fault in the Sea Class, but doubts do remain as to whether there is a large enough market for such a ground breaking amphibious car. "Water" dilemma for Mercedes.