RARE, it seems, is the big-money public project in the UK that can be brought in on time - and, more crucially, on or even under budget.

There has been a grim litany of prestigious developments that ended up costing far more public money than had been originally envisaged.

Successive delays and staggering cost overruns have affected the high-speed rail project, HS2, completion of which is now up to two decades away. Costs have doubled from their initial estimate. Some £190 million is said to have been wasted on unnecessary work on another rail project south of the border, the 76-mile Transpennine line.

Huge sums of public money were squandered on procurement projects when the UK government sought - admittedly during an emergency unprecedented in recent times - to respond to the Covid pandemic.

The Taxpayers' Alliance, writing in 2019, analysed 10 recent and in-progress UK major government projects and discovered that overruns had grown to a total of 32.7 years and £17.2 billion, or £624 per UK household. That £17.2 billion overrun could have paid for seven of the 10 projects at their initial cost estimates, with £4 billion leftover, the group added. It said that numerous studies had suggested that costs were intentionally underestimated to secure project approval.

Scotland has not of course been immune to cost overruns. Prior to the referendum of 1997, there was an early estimate that it would cost between £10 million and £40 million to build a home for a Scottish Parliament in Edinburgh. The final figure was some ten times greater. The cost of the Edinburgh trams project was initially put at £375 million, back in 2003; the total would eventually soar to £776 million, and the development was finished five years late.

Read more: SNP ministers feared they were being misled over Edinburgh trams

The problems surrounding the two ferries at Port Glasgow are a classic case-study on their own. As Audit Scotland remarked more than a year ago, the total cost of the ferries project was currently estimated to be at least £240 million, around two and a half times the original contract price.

And now, to no-one's lasting surprise, the cost of building a long-overdue replacement for Barlinnie Prison is now generating controversy, with First Minister Humza Yousaf needing to promise to investigate an estimated £300 million overspend. Meantime, a new prison in the Highlands is expected to cost around £140 million, a steep increase from its projected £52 million in 2011.

Not without some justification, Mr Yousaf has pointed to a rise in construction costs, caused by UK government actions and by Putin's invasion of Ukraine.

Read moreHumza Yousaf to probe £300m extra costs in replacing Barlinnie

Generally, ambitious, long-term projects are originally costed at then-current prices, with the costs subsequently at the mercy of runaway inflation. Specifications being altered during the construction phase can also have an adverse impact, as happened with the ferries. Some projects, as the economist Tim Harford has noted, often unfold in an haphazard way.

There has, furthermore, been a massive increase in the costs of building materials, attributable to various factors. Some of them are related to Brexit, as a lot of the materials arrive from mainland Europe. The weakness of the pound means it is so much more expensive now to import. Labour shortages in construction have pushed prices up, both in terms of paying staff directly and in the cost of using sub-contractors. But such causes surely do not account for the staggering rises we have seen in some projects.

At a time of high inflation, acute pressure on public finances, and a draining cost-of-living crisis affecting millions of ordinary people, a greater awareness is needed of potential cost overruns in what might be dubbed mega-projects. Greater rigour is essential, not just when it comes to formulating contracts and to seeking expert external advice, but also in parliamentary scrutiny. Looking at how similar projects were tackled overseas might be a help, too.

Big cost overruns are not of course the exclusive preserve of the UK. Examples abound abroad. It took fully 30 years before the last debts arising from the 1976 Montreal Olympics were paid off, with a huge overrun on the stadium constructed for the Games.

Planners of big projects at home and abroad could do worse than to read the latest book, How Big Things Get Done, by the Oxford University academic Bent Flyvbjerg, who with colleague Dan Gardner has examined megaprojects across the world. To ensure that project begins in the right way, Emeritus Professor Flyvbjerg advises, it is essential to ensure that good funding and a good team are in place. "You get the front end right", he said this week, "by asking questions - 'why are we doing this project?' ... 'what is the basic need that we're trying to meet here?'" It is little wonder, he says, that only about 8.5% of projects finish on time and on budget.