Just what has been the cost to construction of the recession? Could and should policymakers have made the slump in activity less painful? Were there better policy options?

These questions need desperate attention. Mistakes were made. Bad and avoidable mistakes, in my view. Lessons must be learned.

Construction is a strategic industry. Having a construction industry is not an option for any nation. That makes it special, like health, education or defence.

Recessions can disproportionately hit construction. The damage, however, will eventually need repairing and that comes at a higher or lower future cost depending on policy decisions made when the recession bites.

In any sensible world, policymakers would estimate that cost and factor it in before deciding whether to cut or boost public investment and whether to incentivise or not private investment. They should be aware of the cost of recovery when assessing the value of investing in the fruits of construction.

From what I have observed over the past six years, I doubt that crosses their minds for more than a fleeting moment.

So let’s see if we can start exploring what damage was done and put a figure on the cost to put things right, even if we start from back-of-an-envelope sums.

The severity of the damage caused to construction by the Great Recession is patent. Two impacts on the UK industry are hard to ignore. They are currently a source of grave anxiety for businesses and policymakers. The loss of skills, or human capital as economists might describe it, has been huge. The depletion of physical capital and capacity within the whole supply chain is significant.

There has been, however, massive but less immediately evident damage caused by half a decade in an economic quagmire. The construction industry’s reputation, never that splendid, as a career choice for young folk has once again been tarnished. And a particularly worrying concern must be the potential damage to UK contractors, particularly large firms, caused by six years of less-than-prudent bidding.

It was all rather predictable, but the fallout from imprudent and suicidal bidding is yet to be realised and is very unpredictable. Many contract periods are long, so the final bills are yet to be settled. And the final settlement on a contract is far less straightforward than many might suppose. While the effects are being seen in the accounts of contractors, it will be sometime yet before we can measure the full damage.

As Warren Buffett would say: “Only when the tide goes out do you discover who’s been swimming naked.”

The cost to repair the damage to corporate structures is hard to assess. There will be loss of goodwill, expensive restructuring and thousands upon thousands of hours spent sorting out the mess. Organisation knowledge will be lost as yet more human capital is thrown to the wind. On the upside, change might force some improvements.

In finding a figure for the cost, it might be worth starting by examining human capital. The concept may seem a bit wishy-washy, so it might be instructive to see the estimates by the Office for National Statistics. ONS estimates the loss of human capital between 2008 and 2012 was £1.1 trillion. Falling from £18.2 trillion to £17.1 trillion

Just playing with the figures and assuming human capital were spread evenly among the nation’s workforce, which it isn’t, the value of the human capital in construction in 2007 would be about £1.18 and in 2012 about £0.93 trillion. That would be a loss of £250 billion.

The scale is mind-boggling. Now while this huge figure may be within an order of magnitude of the loss of human capital to construction, it’s clearly miles away from the replacement cost. Most human capital is accumulated out of the workplace and work-related training, but much is associated with working.

A more pertinent question might be how much would it take to train a replacement for each worker lost to the industry? We should be able to come up with some reasonable guesstimate figure for this.

I was given for a blog some years ago a rough-and-ready figure of £30,000 for the total cost to train person and provide on-the-job experience from scratch to become skilled in construction. It must be remembered that formal training is just part of the cost. Skills are acquired over time when productivity is lower than it might otherwise be and supervision higher, representing a cost to the firm.

This figure can only ever be crude given the range of skill levels and ages within the industry. It is probably light when all costs are taken into account and the cost to train senior people will be much higher, but let’s work with it.

The costs associated with raising human capital are generally absorbed in the normal scope of business, they may attract grants, but the process is in normal times generally a continuous one.

However the industry lost about 400,000 people to the recession. Much human capital was lost for good, much was not replenished as it would have been, which means the industry would have made savings through the recession on training costs.

But now for the flip side. Filling the gap that is left, if it is to be done without a huge influx of foreign workers or be overcome through innovative building techniques, will now mean an expansion of training, formal and on-the-job. This will cost the industry, based on our estimated average figure, £12 billion. No wonder “importing” skilled workers from Lithuania, Latvia and Poland looks attractive.

We can do similar figures for physical capital. Let’s look simply at some figures for net capital investment for the construction materials suppliers from the Annual Business Survey (many thanks here to Dr Noble Francis and his team at the Construction Products Association for the base data).

Ignoring 2008 as it represents a transition into recession, the estimated average net capital investment in the years 1997 to 2007 was £1.41 billion. The figure 2009 to 2012 was £750 million. That means there was an average annual drop of about £660 million. The 2013 provisional ABS figures don’t suggest a major recovery in investment.

A rough count would suggest that over the five years 2009 to 2013 inclusive, the total net capital investment was £3.3 billion less than it might otherwise have been. An investment more or less of this scale will be needed to bring things back to where they were in the material supply sector before the Great Recession.

We then need to consider the collapse in capital investment by contractors, by plant hire firms and by the distributors. The damage to the industry’s infrastructure here will also have to be rebuilt if construction firms are to deliver as effectively today what they could in 2007.

It would not take much consideration of these and other factors before we might reasonably estimate the degradation of the industry from recession will cost at least £20 billion to repair. That’s about £300 per person in Britain and this leaves aside the damage caused to the image and reputation of the industry.

To put that £20 billion in the context of the industry itself, it is about 10 times the total pre-tax profits made by the top 100 contractors in 2007.

Now you can quite rightly argue with these figures. You may feel they wildly underestimate or wildly overestimate the challenge. But it’s hard to dispute that the recession has left the nation with a huge bill to pay if it the construction industry it desperately needs is to be restored to what it was before the Great Recession.

Now ask yourself, was it such a good thing for the government not to invest more heavily in construction when the recession hit?

As I hope to explore in future blogs, there were clear alternatives, what’s more they could have made and saved the government money and, ultimately, reduced the nation’s debt.