If a car can cope with the gridlocked streets of London, there’s a fair chance it will handle most other things. So, the start of the Opel Fuel Cell Marathon’s eighth leg was crucial, and there was heavy traffic as the Zafira edged out into the city’s crowded streets.

The GM project engineers had already explained how rigorous pre-marathon testing had included high altitudes, freezing conditions and stifling heat – now it was broken tarmac and stop-start traffic. After an hour we had covered a mere 18 km, but had successfully negotiated Hyde Park Corner and stopped for a quick photograph outside the world famous Harrods department store.

As we reached the edge of London traffic cleared and the Zafira, Vauxhall-badged for this stage of the event, was able to stretch its legs. In fact, the convoy made such good progress on the motorway down to Dover it arrived in time to catch an earlier ferry across to Calais.

When planning the route, the team had originally planned to make the crossing by train. A shorter crossing time would have been a bonus, but Euro tunnel wouldn’t allow the HydroGen3 vehicle through. This decision highlights another obstacle car makers must overcome in a bid to make fuel cells viable commercially. Many still believe that hydrogen is a dangerous fuel.

In the event, the ferry crossing was smooth and the team, fed and watered, were soon cruising along a smooth French Autoroute. But not for long. By mid-afternoon it was the turn of the Zafira to get a refill of its own. The first stop took place at 156 km with further halt that evening, shortly before Paris. By the second stop, the fly-spattered blue and white car had covered 318 km, but was still performing well. A coolant level warning light was the only excitement, but this was caused by a faulty sensor and didn’t slow down our progress.

The convoy arrived at its destination shortly after 7pm, having added another 405km to the total. Larry Burns, GM’s vice president for Research & Development won’t be satisfied yet though. "The real winner will be the first company to build a million fuel cell vehicles profitably," he had told students attending a lecture the previous evening in London.

On this evidence you wouldn’t bet against GM achieving this. Especially if, as promised, the next generation of cars will be able to offer improved performance, handling and, importantly, range.