Chris Rayner strides across a large but almost empty room to join us in the corner where a couple of workstations stand, with two more taking shape alongside. This is the operations room of the Thames Valley Signalling Centre in Didcot, which opened at Easter.

If all goes to plan, by 2018 it will be a hive of activity, the ‘brain’ of the network in the region and beyond, controlling trains from London Paddington out to Bristol, Westbury, Oxford and Worcester.

The centre accounts for a small but vital part of a projected £5bn of investment to modernise the Great Western mainline and its connecting routes, increasing capacity and cutting the cost of running the railway.

Mr Rayner, Network Rail's western route director, is enthusiastic about the possibilities: “What I want to do is fill this place up. If we put a desk in here, we’ve potentially got half-a-dozen signalboxes out there which we can close. The saving is large.”

He is an unabashed advocate of progress: “I consider myself to be a very modern sort of railway person and I’m not all that bothered about the heritage, but occasionally, I have to be sensitive to it. It’s ingrained in the DNA down here.”

That is partly the result of Network Rail being the custodian of Isambard Kingdom Brunel’s original GWR route, which the Government is considering nominating as a World Heritage Site. Tuesday marks the 175th anniversary of its founding, with a series of events at Didcot and steam journeys on offer.

Mr Rayner thinks he knows which side the great engineer would have been on when it comes to improving the system in the 21st century: “I should imagine Brunel, as the original railwayman, would have been a passionate advocate for the railways.

“I’ve been in the industry since 1975 and in the first 10 years of my career, it was all about contraction and cutting, concreting over railways and putting roads in, because everyone thought railways were a dead loss and the car was going to be king.

“So Brunel would have been disappointed that his legacy was disappearing and I imagine if he had been around now, he would be immensely optimistic, because things have changed completely. It’s a great time to be in the industry. We are running more trains, with better punctuality, more rolling stock and more money being invested. And we have got a Government saying it’s got to cut 25 per cent of its expenditure but still talking about building a high-speed railway and not talking about building motorways. You have got to pinch yourself.”

While rail passenger numbers fell once the recession began in 2008, they have since bounced back and new freight customers are signing up, including a major supermarket chain, which is set to switch its long-haul distribution from road to rail to cut its carbon footprint.

The elephant in the room is the Government’s comprehensive spending review. Mr Rayner said: “It’s the Government’s choice. Based on what happened prior to the recession, that growth will continue and there’s a point very soon, depending on which figure you look at, when the Great Western main line runs out of space — then what do you do?

“Either price people off the railway — and that’s a very brave thing to do politically — or you build more capacity, don’t you?”

Work under way to increase capacity includes the £67m project to redouble much of the Cotswold Line between Oxford and Worcester, due for completion next year, and the £400m Reading area modernisation over the next six years. Signals in the Berkshire town will be operated from Didcot after Christmas.

“In terms of capacity, Reading is the most important project we’ve got, along with Crossrail [to create an east-west tunnel under central London],” said Mr Rayner. “Reading unties the knot, adds extra platforms and improves the eastern and western approaches. It’s fantastic and that kind of thing puts us on a good footing for growth for a number of years.”

In July last year, the previous government announced a £1bn project to install overhead electric power cables from London to Oxford, Bristol and South Wales, but this is among spending being reviewed by the coalition.

Mr Rayner said Network Rail was lobbying to keep the electrification plan alive, which would also mean new signalling and trains.

He said: “We think there’s a good case for electrification here. If it’s not affordable, there are ways of skinning it. People are already mooting doing it in a different way, maybe doing the inner sections first.”

He added: “We’ve got more investment now than we’ve ever had and clearly in the current environment it’s got to be subject to review.

“You could go back, you could stop spending. In the 1970s and 1980s we weren’t spending anything and the railways were deteriorating.

“With an asset like a railway, you can do that. You can probably do it for a few years, but it’s then really difficult to pick it back up again, because all these billions of investment and the people that are doing it, they don’t hang around and wait for work.”

Network Rail is well aware that it will not get a blank cheque. The bill for running the system is worrying the Government and the Office of Rail Regulation.

Mr Rayner said: “They are concerned about the costs of the industry, because they have rocketed, and they’re concerned about the take from the farepayer, so I think we agree structurally something has to happen. I don’t think anybody really knows what yet.”

He added: “We can do more on efficiency. Between 2003 and 2008, we took out 24 per cent of our costs and we’re committed to taking out another 21 per cent by 2014, so that’s not bad going. The message we’re getting is that despite all that, the country can’t afford the railway it has got. I’m not sure it can afford not to have the railway it has got.”

As for the possibility of another overhaul of the relationship between the Government, Network Rail and the train operators, Mr Rayner said: “We’re up for the discussion. We just think — and it’s not just about turkeys not voting for Christmas — that if you radically change the structure of the railway and throw it in the air again, you will put us back five years or even longer.

“We talk about a railway renaissance and get dewy-eyed about it but it’s true, it really is. This is an incredible time.

“I’ve never seen so much money being spent in this industry and that’s what’s at risk. Because all this is happening very quickly, with a change of government and a complete change of policy, it’s a very short timeframe to be having these very, very big discussions and we’ve to get our voice heard.”