Research by the RAC Foundation reports that 199 out of 605 such structures in Britain require intrusive so called Post-Tensioned Special Inspections (PTSIs), that can cost £100,000.

These structures, while not technically comparable with the bridge that collapsed in Genoa, Italy this summer, do feature hidden cables like the Morandi motorway bridge.

“Thankfully no one believes we are on the brink of a catastrophic failure in this country but to be 100% certain we need adequate inspections, and those require adequate funding,” said RAC Foundation director Steve Gooding.

The report estimates that funding required to carry out all the required PTSIs could add up to £21.4M.

“A full structural risk review needs to be done for highway bridges normally at principal inspection stage every six to 10 years, but the survey indicates some may not been done for at least 18 years,” said ADEPT national bridges group chair Kevin Dentith. “I’m sure these post-tensioned bridges aren’t a major risk; they will be having routine inspections. But a programme of more intrusive inspections does need to be considered for those that have not previously had a full PTSI.”

He added: “Hopefully some of the Department for Transport’s £200M Challenge Fund set aside for 2019-21 will be used to prioritise this work. We should find out more about how the money will be allocated early this year.”

Further results from the research indicate that 4.4% of council managed bridges (over 1.5m in span) are ‘substandard’, meaning they are unable to carry the heaviest vehicles permitted on the network, which are lories of up to 44t.

The one off cost of clearing the maintenance backlog for these 3177 substandard structures in England, Wales and Scotland currently stands at an estimated £6.7Bn, up from £5Bn last year.

“Substandard does not mean the bridge is going to fall down,” said Kevin Dentith. “Bridge maintenance is about priority. In large rural counties like my own authority, Devon, there will be structures that on paper fall short of current design standards, however they are never likely to be strengthened because the load capacity is adequate for the location.

“It’s only those hampering traffic movements on significant routes or those linking communities that seriously need to be addressed, the rest can be managed and given acceptable weight restrictions.”

Steve Gooding added: “Ancient bridges on rural back roads might not be the highest priority for repair, but the risk we run is that sub-standard structures on some roads result in heavier vehicles having to make lengthy detours.”

Between them, councils say they would ideally want to bring 2026 – or 64% – of the substandard bridges back up to full carrying capacity. But budget restrictions mean that only 343 of these are likely to have the necessary work carried out on them within the next five years, they add.

Despite financial pressures, annual expenditure by councils on maintaining bridges rose from an estimated £367M in 2016-17 to £598M in 2017-18.

(Photograph: Alastair Lloyd)