At 357mph, it was impossible to focus on anything within a mile of the train.

Even distant hilltop villages flashed past in a second. The sense of flying across the landscape of the Champagne region was accentuated by being on the top deck of the doubledecker TGV train.

Engineers had laboured for months to ensure millimetre precision in the track geometry, but we still lurched alarmingly. For one terrifying moment, the traine even seemed to rise from the tracks.

We were travelling twice as fast as a passenger jet on the point of take-off, but there were no seatbelts. At that speed, they wouldn’t have saved us anyway.

As the only British journalist on board, I was determined not to show how frightened I was. The assembled French media, politicians and rail bosses seemed to love every second and showed no trace of fear.

But then they have absolute faith in the safety of their high speed lines, with no passenger fatalities in 26 years of operation. I have reported on six crashes which have killed 60 people on Britain’s so-called fast lines in just the past decade and none of the trains was going faster than 125mph.

The most disturbing thing was not knowing how fast we would go. There had been rumours that the French would try to exceed the 361mph achieved by a magnetically levitated Japanese train. But the maglev floats above its concrete guideway and is far smoother and quieter than wheels on rails.

The speed was displayed in kilometres on TV screens above our heads and there were cheers as we broke 500kmh. The cheers grew louder as we edged past the world record, set by a TGV in 1990, of 515.3kmh (320mph).

Then an extra surge pushed us quickly up to 570kmh. We hovered around that speed for about two minutes as the driver seemed to seek one final burst of acceleration. A camera on the roof showed white flashes on the overhead powerlines, from which we were drawing 19.6 megawatts, more power than all the cars which start a grand prix race.

The sense of being on the edge of a void was heightened by the knowledge that, in test runs, this train had taken 10 miles to stop after the brakes were fully applied at just 514kmh.

There were 40 technicians on board, but none of them could tell exactly how the train would behave above 350mph, especially with a fairly strong crosswind. When we slowed to 200mph, which will be the standard speed when the new Paris to Strasbourg line opens for service in June, it felt like a jaunt on the St Ives branch line.

The record had cost €30 million to stage and taken a year to plan, but none of the French media asked questions about cost. No one even mentioned that the €5 billion TGV Est line had been approved despite official predictions that it would never make a profit,

Our souvenir tickets had “L’excellence Francaise” stamped across them and it would be impossible to put a price on the national pride beaming from every French face on board and reflected in those of the thousands who lined the route.

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