England is broader than it is long, at least in travelling time, and it is not looking good for this Cornish lifeline that trundles for eight hours and twenty minutes to the far-flung extremity of the land at Penzance.

Gradually, out of the half-light of Brunel’s great train shed, passengers begin to appear. Most have booked; some just turn up in the hope of a bed. All are found a berth by Linda Ryder, the train supervisor with a clipboard and smile.

One man, on his way to a day’s business in Cornwall, discloses that he missed the evening flight from Stansted to Newquay by minutes. He knew nothing of this overnight alternative until airport staff suggested he try Paddington.

Slowly the train fills up. By the time we pull out, on the dot of 11.50pm, 54 of the 64 berths are occupied. “Normally we are full on Thursdays,” Linda said. “Must be because it’s the week after half-term.” I have bought, on the day, a first-class return for £112.85, plus £36 sleeper supplement. Booking early, I could have had a standard-class single fare for only £34. This service loses £1 million a year, and the rail regulator is casting a menacing eye over its future. By next April it could be no more.

Most passengers have retired behind closed doors, but a hardy few sit up in the buffet car, where the waitress is doing a sluggish trade in nightcaps. Stuart Smith, a heritage consultant, has just flown in from Tokyo, and is tackling his own bottle of Suntory whisky.

“I use this service once a fortnight and it’s a godsend,” Mr Smith said. “The cost is irrelevant; it’s all about convenience and saving the need to spend an expensive time in a London hotel. The train drops me almost at my front door in Camborne in time for breakfast.”

His companion, a public services officer in Truro, argues that communications to the far West are improving in some way. “The notorious bottleneck on the A30 at Indian Queens should be gone within two years, but if you have a meeting in London you’re not going to drive all that way,” he said.

The sleeper means you can be in London by 8am, do a full day’s work and catch the last day train back at 6pm. The fastest day train takes five hours in either direction.

Jennie Crewdson is a specialist physiotherapist who lives in Newlyn and works four days a week in London. “I can go up on Sunday night and come back on Thursday,” she said. “Without the sleeper I’d have to sell up in Newlyn and live permanently in London.”

We have been going 45 minutes and are still only at Reading; but there’s no rush; the Night Riviera takes its time to give its passengers a better chance of a restful night. Within another hour the train’s buffet car and corridors are eerily deserted, and all the noise comes from within my cabin. Another half-hour is taken up with identifying a cacophony of minor rattles; the main culprit, the fold-down shelf for the breakfast tray, is eventually identified and silenced.

Taunton is the first stop. Two passengers spring from their bunks for a five-minute break on the platform; not for a sniff of the early morning air, but for a smoke. Since a fire on board in 1978 that killed 11 passengers, the sleeper is very strictly non-smoking.

Sleep is fitful. Although the berth is long enough for a six-footer, it is not wide enough to permit more than a half-roll-over. Still, it is bliss to one who has spent too much time trying to sleep on economy-class overnight flights.

The rhythm of the train eventually becomes soporific, leading to thoughts of W. H. Auden’s Night Mail.

Two solid hours of rattle-free unconsciousness destroy the good intention of being awake to enjoy the most scenic part of the route, where the track follows the sea wall at Dawlish. Still, there is always the view as the train takes a tight curve on the approach to Brunel’s bridge over the Tamar just beyond Plymouth. Bother, missed it; we are in St Austell already.

No chance of sleep now; the rhythm is destroyed by the train’s frequent stops down the spine of Cornwall. A knock on the door from Linda brings orange juice, tea and an individual packet of cereal. It may not be much, but have you ever tried what some airlines try to pass off as breakfast? The Night Riviera draws up to the buffers at Penzance dead on time at 8.08am. Cornwall’s overnight lifeline is punctual and clean, with a pleasant and attentive crew and a bar that stays open most of the night if you want it. It is not the Orient Express, but it is relatively cheap, more ecofriendly than cars or aircraft, and needs Cornwall's phalanx of Lib Dem MPs to stand up for it.

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