It's unlikely that you will spot Dave Repton at work. Dave, 36, has worked for half his life as a relief signaller on the Settle-Carlisle railway line.

Not quite so cut off from contact with the outside world as, say, a lighthouse keeper, manning a signal box in this remote patch makes the job essentially a solitary one.

"You don't get to see many people," concedes Dave. "You talk to people on the radio and on the phone, but you could walk past another signaller in the street and not know it was them unless you heard them speak and then you'd think, 'I know that voice'."

No-one is allowed into Dave's workplace without permission. "The only person who could come in without an appointment would be the railway chaplain. You can talk to them about anything – not just church matters, but anything that might be bothering you in your personal life."

Dave can be called out to work a shift at any one of six signal boxes on the line – Kirby Stephen, Appleby, Kirkby Thore, Culgaith, Low House and Garsdale. "Garsdale is my favourite. The views from there are really breathtaking. On a clear day from the signal box you can see for miles. It's interesting because although you are in a very isolated location, there are always people on the platform. It's a working station. That's unusual. The only people you see at Kirkby Thore, for example, are the shunters because you are in a siding of the main line."

Dave has been in the job since he left school at 18. "It's a job for life – well at least it was in days of old. In an ideal world, I would like to be here until I retire, but there are fewer signal boxes now and a lot more computerisation."

A computer on Dave's desk at Kirkby Thore records trains' movements. A handwritten log is kept as back-up.

"Your job is to see the train along your bit of line safely. I accept a train from the previous signaller, then I offer it up to the next signal box on the line; they accept it and then offer it up to the next one along. It's like a gigantic game of pass the parcel.

"You can't think at the end of a shift, 'I could murder a pint' – you just can't do it because you have to be up early the next morning and with a clear head. So there is a certain amount of discipline and regimentation. But I like the fact that I am in such a trusted position.

"Some of the signal boxes have push button signals, but most of the ones I work at have levers. Some of them are hard to operate – it depends on the distance of the signal to the signal box because by pulling down on the lever you are literally pulling a piece of wire to get the signal in position. You have to be physically fit, but there is a knack to it.

"The winters are nothing like they used to be and we don't get the level of snow that we did. If there is a problem – such as a snowdrift – we have 'ship to shore' radios so the train driver can contact us and vice versa. What happens up here quite regularly, though, is sheep on the line. The bridge at Kirkby Stephen often gets hit by high-sided vehicles. Then you have to close the line down until someone has been to examine it and check that it's okay."

They have what is known as an absolute block system (it dates back to the 1880s) allowing only one train in one section of one line at any one time. Even so, accidents do happen.

"There was an accident at Aisgill in 1995 when a guard got killed. That was very upsetting. I wasn't involved at all but it does shake you up." In 2004 at Tebay, four line workers were killed when they were hit by a runaway trolley. "That one really did sting. I knew one of the guys quite well and I had only seen him and been talking to him about a week before the accident."

Dave's father was also on the railway. "He worked at Aisgill signal box for a while and then in track maintenance for 35 years. My uncle was on the railways, too, for 30 years. My dad didn't like being stuck in a signal box, he preferred being outside. I happen to like it.

"You need to like your own company. You are basically on your own 12 hours a day. You have to be a certain type of person to be able to cope with that and you have to think of it as a way of life, not just a job.

"The regular guys know what they are going to be doing for the next few months, but I like the variety. That's why I chose to do relief work. I have never been a trainspotter, but it is nice to see the old steam trains coming through."

In the quieter signal boxes, signallers are permitted to read, or to listen to the radio. Every box has bathroom facilities, cooker, microwave, fridge and water cooler.

They are heated, which means in winter they are quite cosy. "In summer, though, they can get very hot. With all the windows, it's a bit like being in a big greenhouse."

Dave admits that there is a certain amount of stress involved in his work – "It is demanding and if you do something wrong, you could end up in court" – but for all that, he seems quite content.

"Yes," he says looking out at the view over Dandry Mire and its viaduct, "I am very happy in my job."