UNDERNEATH the city at midnight and teams of workers are grafting in the Subway tunnels.

It is the side of Glasgow’s underground most passengers will never get to see.

Every night, once the trains stop running, up to100 construction workers and engineers head down the tunnels where improvement works are transforming the network.

The last major improvements were carried out 30 years ago but the men who worked on the tunnel then would recognise the work being done now.

And so would their Victorian forebears, the men who, 120 years ago, built Glasgow’s Subway network.

Stephen Shannon, infrastructure production manager, has taken me to Govan station where we meet up with a “loco” - a battery operated cargo train carrying everything needed for the improvement works.

This includes the heavy steel rails to replace the tracks. Workmen use pulleys and rollers to lift them off the loco - which had no roof or solid sides - and on to the floor of the tunnel.

Mr Shannon said: “It does involve a certain level of physical fitness but it is an accepted part of the job.

“Over the years we have looked at everything that is available on the main line but we always come up against something that thwarts us from using it.

“And, as you can imagine, there’s a lot of fancy kit out there but we just can’t introduce it into our system so a lot of it is quite basic.

“We look at old footage and we look at what we do now and it’s not that different.

“We don’t really want two guys working between two trains but we haven’t come up with anything better.”

All the work carried out in the system must occur overnight in order to keep the Subway operating, putting immense time pressure on the crews.

Mr Shannon added: “We have a window of five-and-three-quarter hours to get work done but because everything has to be delivered at the beginning of the shift and taken away at the end, there’s really only four-and-a-half hours for work to be done.

“For the last hour of the shift they must be able to make the track safe for passengers again.

“They always have their eye on the clock.”

The tunnels lie between between seven and 115 feet below the Clyde’s high water level and being so close to the water means ingress is a problem in places. Part of the works include improving the pumping systems, to try and counter this.

In one section of the tunnel, the roof is riveted metal archways with what look like stalactites hanging down.

Mr Shannon explains these are made of sediment-filled water that has leaked in to the tunnel and solidified.

In another section we visit, the tunnels are completely different - made from concrete.

Civil engineering firm Freyssinet is a contractor for tunnel lining works with staff spraying concrete on to the tunnels.

They aim to cover five to six square metres a night, but it can vary.

Shift manager Garry Boyce said the firm has hired 80 local young men to work on the project.

He said: “Quite a few of the boys had never worked in construction before and have been with us for almost a year now.

“We have been really lucky with those we have taken on from the local area - they have been fantastic.”

The works are a £16 million programme of tunnel improvements from Strathclyde Partnership for Transport (SPT), which runs the Subway.

Each station and section of track presents its own unique challenges.

At Cessnock, for example, the tenements are so close to the Subway that work on the tunnel roof exposed the floorboards of the flat above.

Charlie Hoskins, senior director at Strathclyde Partnership for Transport (SPT), said: “I don’t think it can be underestimated how tricky it is to do that kind of work.”

The tunnels are an almost female-free environment. Freyssinet has one female engineer working in the tunnels, seconded from its offices in France.

Mr Shannon said there has been one female worker down the tunnels who “more than held her own and opened the eyes of quite a few of the guys.”

He added: “We had hoped that would open the floodgates but she moved on and we haven’t had any female workers since.

“But we would be keen to see more.”

One of the Freysinnet staff insists the tunnels are haunted and that on occasion workers know the ghost is there because they can smell lavender.

I’m not convinced by his ghost story, but it is certainly an eerie environment and one that has been fascinating to see.