To me, Blea Moor Tunnel, just north of Ribblehead, is the most impressive piece of work on a railway that broke records. The Settle -Carlisle line, middle route to Scotland, climbs gamely from the limestone reaches of North Ribblesdale and cuts through high ground to reach the fertile Vale of Eden, with its red sandstone villages and farms.

Blea Moor tunnel, with a length of 2,629 yards, was hewn out between 1870 and 1875 and cost £45 a yard. Dynamite, a new form of explosive, delivered by road, cost the contractors £200 a ton. The tunnel is 400 yards longer than proposed. Otherwise, cuttings on the southern side would have been too deep – a perpetual threat to traffic from landslip.

When I first knew about Blea Moor Tunnel, steam–hauled trains, passenger and goods, were operating with great frequency. I was fond of taking the high track, between heaps of excavated material, to where smoke from locomotives rose up three ventilation shafts. Blea Moor had become Yorkshire’s Smoky Mountain! Early on a Sunday morning, 54 years ago, when I travelled to Blea Moor with the prospect of walking through the tunnel, I saw a Misty Mountain – mist so thick it verged on drizzle.

I headed for the northern end and met Mr A Gardiner, chief works inspector. Railwaymen were sipping mugs of hot tea before venturing underground. The inspection work would take place on the “up” line, currently out of service. On the closed line stood a cattle wagon adapted as a platform from which men, with spears on long rods, might study the tunnel head and sides at short range. The spearheads were fashioned from worn–out shovels. An attached wagon held wedges, cement, sand and bricks. A seated inspector had writing materials to record any needful jobs.

Blea Moor Tunnel had a crown, haunches and sidewalls. Tablets on the sidewalls noted the distance from the tunnel mouth at the southern end. Any part of the masonry might have its location noted exactly. From high above the tracks came the chanting of the men who were reporting on the state of the masonry. “Hold it, lads,” came a muffled shout – and some soft masonry was brought down while the position was noted so that it could be repaired.

The wagons rumbled through a gloom that was relieved by paraffin lamps. I walked close behind and in the company of Mr JE Turner, an engineering assistant. He rubbed a finger on the masonry, revealing a mixture of soot, mud and water. One of the railwaymen said: “Thee wait till we have diesel trains. When they’re rattlin’ about we be able to whitewash the tunnel out.”

At the bottom of shaft No 3, which is 10ft in diameter, I had the novelty of looking upwards for 390ft, the distance from rail to moor. This shaft was 50 feet deeper than that of the main chamber of Gaping Gill, the huge pothole on the flanks of Ingleborough. The Blea Moor shaft was wondrously masoned. It (and the other two I would see later) were marked at intervals by “garlands” that intercepted rainwater and led it into a fallpipe, which in turn poured into the main drains of the tunnel.

From far up the tunnel came three blasts on a whistle. “Train on the down,” someone yelled. I felt compression on my ear–drums. There was a shriek from the locomotive, a sound that reverberated through the huge cavern. “Clear the six–foot,” came another anonymous voice. There was always a danger that the sheet on one of the passing wagons would be flapping – hurtful if a man was struck and the train was moving at 50 or 60 miles an hour.

I heard another whistle from the train. This time it was much nearer. A giant locomotive thundered past only a few yards away from where we stood. Firelight stained the darkness. I heard the staccato clattering of wagons. Then silence – a silence intensified by smoke that billowed down from the head of the tunnel, blotting out the friendly circle of light – the tunnel mouth or a ventilation shaft.

The moaning monster had seemed to fill half the tunnel to within a few inches of the roof. It was travelling fast enough to draw most of the smoke behind it. My engineer friend had suggested in advance that I should tuck my trousers into my socks “or you’ll have smoke pouring from under your collar.” An anonymous voice shouted to the men: “Hod it while it clears a bit.” The work was resumed after five minutes.

I chatted with Derek Soames about his 1975 walk with his son Michael from Settle to Carlisle. I was keen to know if they, with permission, had walked through Blea Moor Tunnel. They had, having previously checked with the signalman at Blea Moor box that the line was clear. Derek worked as a platelayer in the 1960s. He knew to go on a Sunday, when there was least traffic.

His special recollection of the tunnel wall, against which – in his early days – he leaned when a train was due, was that he was “covered in wet soot from head to foot.” He had known Blea Moor when it was in utter darkness. “The generator working the light had broken down. It was pitch dark. All we could do was stand until someone got the generator going again.”

I saw few features in Blea Moor Tunnel apart from the brickwork. One redundant item, part of which survived, was a huge gong that was operated by a train as it entered the tunnel. I was amused to see a rock cavity called The Donkey Hole, used during the construction period. The cheerfulness and skill of the railwaymen impressed me. In six years of hard, smoky work they had re–lined a considerable part of the tunnel.

Said one of them: “Tha’s bin lucky today. When thou gits home tha’ll nobbut need a wesh. Most days we need a bath – and we’ve to change t’watter several times an all.”