I admit, my tastes might be slightly specialist. I love visiting construction sites. I’m a member of a group called Subterranea Britannica devoted to the appreciation of man-made tunnels. And I enjoy little more than the thrill of standing on bridges over TGV lines, watching trains speed by at 180 miles an hour underneath.

So you might want to ignore everything I say about infrastructure. I’m clearly a fan. But it’s one of the hottest topics in policy-making circles at the moment, and I’ve had a chance to reflect on it in recent months, making a two-part BBC2 series on the subject.

The filming has not just provided an excuse to get down and dirty with some of the best of British infrastructure – from the magnificent views on top of the Forth Bridge, to Hinckley Point B nuclear power station, to the London Array, soon to be the world’s largest off-shore wind farm. The series has also afforded an opportunity to ask whether we invest enough in it and whether we are much good at delivering it.

My main concern has not been the short term boost that infrastructure investment can provide to a moribund economy today, but the long term character of the country. The choices we make today on how much to invest and where, will help shape the economy we have over the next few decades.

First and foremost, infrastructure has the potential to provide space for growth. In front of me as I write this is a ball of clay, a souvenir I brought with me from an extraordinary trip I made while filming for the series on Phyllis. She’s one of the tunnel boring machines for Crossrail, the new railway line which will run from West to East right across London. Even as you read this, she’s burrowing her way from just outside Paddington towards Farringdon, building around 100m of tunnel a week. But what that line is doing, is giving London room to grow in response to a demographic surge – the population of London is projected to expand by just under 2 million in the next twenty years alone.

But infrastructure doesn’t just have to keep up with change – it shapes the economy and geography of the country as well. Indeed, it has been doing that since the industrial revolution. Britain’s first inter-city railway between Manchester and Liverpool for example, opened in 1830 and was built to carry raw material and freight between the port at one end and the mills at the other. But as with so much infrastructure, things didn’t work out as planned. It turned out that people wanted to travel between the cities too and the railway provided the best means for them to do so (the trains did go at 17 miles per hour after all).

The infrastructure was transformational – the north west of England had suddenly become smaller and new economic opportunities opened up as a result.

Our railway pioneers had stumbled across a phenomenon that modern economists call agglomeration. It is best to think of it as the economic dividend that you earn from bringing people closer together. It is the extra productivity you get by turning towns into cities. As employees and employers cluster, they are exposed to more ideas, more competition and they are likely to find the right personal fit.

Graduate couples for example, are disproportionately more likely to find jobs to suit both in a big city than in a small one. “The large and growing academic literature suggests that doubling city size will increase productivity by 3–8 percent” the World Bank says.

If it worked in 1830, there is every reason to suspect that shrinking distances and expanding travel-to-work areas will give the economy a boost today. That may be an argument for building High Speed 2 or more likely perhaps, an argument for investing in transformational infrastructure across the Pennines (a fast and frequent Crossrail of the north) to make a single travel-to-work area out of England’s great northern cities. If, that is, we have a few tens of billions of pounds to spare.

But agglomeration does not provide the only economic reason for thinking about investing more of our national income in infrastructure. The decisions we make now will shape the economy in other ways too. Where we invest matters? If the capital is to expand as a commercial services hub we need to keep developing urban transport, airports and power and water nearby. If we think that Britain’s manufacturing sector has shrunk too far and will bounce back then we need inter-city transport, freight facilities, ports and energy for other parts of the country.

This all gives us a case for more infrastructure in the south-east, which needs relief from the congestion its fast-expanding economy has engendered. And a case for investing in all the nations and regions aside from the south-east, which could do with the economic development it promises.

But there is a problem with all these arguments for spending more: we don’t really know what type of economy we are going to get. You can just never be sure that the promised benefits of any particular infrastructure project will ensue. Kevin Costner wasn’t right to say “build it and he will come”. Often we build it, and they never show up.

Critics think that is an argument against investing much now, when you can wait to see how things pan out. But as one of the country’s leading infrastructure economists, Oxford professor Dieter Helm, pointed out to me, “If you don’t provide the sort of infrastructure that a manufacturing economy might need, you won’t get one and it will be self-fulfilling. You’ll end up with a London based service economy”. Chicken and eggs abound in infrastructure.

These arguments about the risky choices we need to make are every bit as fascinating as the bridges and tunnels themselves. Funnily enough though, when it comes to infrastructure debate in the UK, these themes are often ignored. The debate is always and everywhere dominated by what one might call local factors. The case for HS2 or Heathrow expansion are debatable (and debated) in terms of agglomeration and Britain’s economic destiny; but I think most people see them as decisions about the quality of life in the Chilterns, Putney, Richmond and Windsor.

Of course, as I don’t have to make a decision on Heathrow or HS2, I’d be wise to avoid expressing a view. But I can offer one interesting observation about local interests from my own personal experience. Opinion is a fickle thing.

I was brought up in Ashtead in Surrey. For much of my childhood our village was terrorised by a fear of a monster that was heading towards us. It was called the M25. Normally upstanding locals set-up a protest movement every bit as active as any in operation today, disrupting a public inquiry with stink bombs and airhorns.

Needless to say, in the mid 1980s, the M25 came along anyway. Ashtead found itself a close neighbour of the new Junction 9 at Leatherhead.

And what do you suppose that the people of Ashtead think about the M25 today? Well, I had a lucky opportunity to test local views by conducting a rather non-scientific show of hands at the annual Village Day this summer. Would you vote to have the M25 disappear if I could click my fingers and remove it? The overwhelming view was that the M25 should stay.

It’s ironic that for all my excitement at the stunning engineering, it was a trip home to Ashtead’s village day which was provided the most revealing insight into Britain’s love-hate relationship with infrastructure.