Unions are warning of public safety risks on Scotland's railways over an "unfathomable" planned cut of £315m in renewing and improving the nation's rail infrastructure over the next five years.

Concerns have been raised by the train drivers union Aslef and the National Union of Rail, Maritime and Transport Workers (RMT) about the planned budget reduction which comes four years after the Stonehaven rail disaster that caused the death of three people.

Rail infrastructure includes tracks, signalling, drainage, earthworks and level crossings - all of which are critical to the safe and reliable running of trains on the network.

According to data produced by the Office of Rail and Road (ORR), the government department responsible for the economic and safety regulation of Britain's railways the planned cut to infrastructure renewals over the five years from April 1 this year amounts to £315m compared to the previous five years - a 13% reduction.

Publicly funded Network Rail, the agency responsible for the upkeep of infrastructure including tracks and signals, has come under increased pressure over the Carmont tragedy, is planning a £2.15bn spend on infrastructure renewals in the next five years.

In September, Network Rail was fined £6.7m at the high court in Aberdeen after pleading guilty to safety failings over the Stonehaven rail crash.

READ MORE: Stonehaven train crash: Union demands that Network Rail 'examine every mile" of Scots track to stop any repeat

The crash, the worst accident on Britain’s railways in 18 years, came after debris had washed on to the track from a wrongly built drainage system after heavy rain. Despite the conditions, the driver was not warned to reduce speed.

Driver Brett McCullough, 45, conductor Donald Dinnie, 58, and passenger Christopher Stuchbury, 62, died when the 06:38 high speed Aberdeen to Glasgow Queen Street train left the tracks after hitting washed-out landslide debris near Carmont during heavy rainfall in August 2020. Six other people were injured.

The Herald: The scene of a rail crash near Stonehaven which killed three people

Network Rail’s fine was reduced from £10m because the firm admitted culpability and a series of failings that resulted in the deaths, pleading guilty to a charge covering the period from 1 May 2011 to 12 August 2020.

In August, last year, a Rail Accident Investigation Branch (RAIB) analysis of 20 official recommendations made over two years ago in relation to the Stonehaven crash showed that just two had been 'closed' or implemented.

The RAIB found that the train derailed because it struck debris that had been washed out of a faulty drainage system constructed between 2011 and 2012 by failed outsourcing giant Carillion.

Aslef has warned ministers in a briefing about the new cuts to infrastructure renewals.

Aslef district organiser Kevin Lindsay said: "If the cuts go ahead, there will be an increased risk to public safety, railway workers and overall efficiency of the service. As the Carmont crash showed we cannot ever take any chances or risk with health and safety and we find it unfathomable that this cut is taking place and will compromise health and safety, as well as making ScotRail more unreliable."

The RMT believes the cuts will not only "threaten services and safety" on Scotland's railways but also thousands of skilled railway jobs across Network Rail and the wider supply chain.

It had demanded that the funding for "safety critical" infrastructure renewals is restored to "at least" the same levels as in the previous five-year period.

In an analysis forwarded to ministers, it said it was important to note that the RAIB report into the Stonehaven train crash found that the failure to ensure inspections were carried out on a drainage system directly contributed to railway engineers not identifying a construction fault which ultimately led to the derailment.

RMT national policy officer Sophie Ward said the union remains "deeply concerned about the programme of renewal and maintenance for earthworks and drainage and believes the funding provided "in no way reflects the risks posed by ill-constructed earthworks and drainage systems and the increase in climate change-related extreme weather events".

The Herald: Handout photo dated 13/08/20 issued by the Rail Accident Investigation Branch (RAIB) of the Stonehaven rail crash which was caused by errors in the construction of a drainage system by failed outsourcing giant Carillion, an investigation has found. Issue

RMT union chiefs in Scotland have previously raised serious concerns over plans to slash the safety-critical maintenance workforce in Scotland from nearly 2000. They have been concerned that 300 Scots maintenance staff with Scottish and UK government-subsidised Network Rail will go in the Modernising Maintenance programme amidst vacancies.

Network Rail has been looking to slash existing maintenance scheduled tasks by up to 50% through what it calls "better use of technology and data", and reducing the number of manual inspections carried out by teams.

The ORR wrote to Network Rail in May about the failure to comply with structure examinations meaning a backlog of thousands of structures on our railway being left with little or no examinations over many years.

The letter stated how this posed a potential safety risk if the backlog remains.

Ms Ward said: "RMT is deeply concerned that a significant amount of risk is being placed upon Network Rail’s maintenance functions at the same time as they are essentially imposing a new Modernising Maintenance agenda that does not have full agreement or buy-in from maintenance workers and will ultimately lead to job losses and a significant reduction in headcount. RMT believes it is highly reckless for Network Rail to be cutting renewals and then expecting the maintenance functions to mitigate the health and safety risks of this of this whilst simultaneously imposing their Modernising Maintenance programme."

The latest cut comes after it emerged that Network Rail received £179m by way of rail enhancement grant from the Scottish Government for improvements in 2022/23.

The Office of Rail and Road (ORR), the government department responsible for the economic and safety regulation of Britain's railways, said that meant that the forecasted grants received for the five year period between April 2019 and March 2024 would be £127m less than previously agreed in a funding letter. This was reportedly due to "wider government funding constraints and slow approvals of projects and release of funds".

The ORR in a June analysis, when £446.7m of cuts were planned said constrained funding "does not need to result in undue concerns for the safety of assets or performance" during the five years "if risks are fully assessed and managed".

The Herald: ScotRail.

An ORR analysis says Network Rail Scotland proposes to use operational controls, such as speed restrictions to manage risks.

It, nevertheless, still anticipated an increase in "service affecting failures" towards the end of the five year period.

In a June assessment, the ORR said: "Our assessment of Network Rail Scotland’s interim plans said: "Our assessment of Network Rail Scotland’s interim plans... has identified that the needs of some core assets in Scotland have not been sufficiently prioritised, particularly metallic structures. We anticipate that the deterioration in asset sustainability could, in turn, impact train performance in future years and present risks to the safe operation of the network."

But in an October assessment when the level of cuts was reduced, it said Network Rail Scotland had developed and is applying a "structured framework that has the potential to identify the best means to safely manage the residual risks so far as is reasonably practicable".

After the Stonehaven crash court case, Network Rail said it would build upon the “significant changes” it had made since the incident, and that about £1.6bn of its budget over the next four years was dedicated to improving the resilience of the railway due to the climate crisis, with rail bosses in Scotland and elsewhere warning that this posed an increasing threat to infrastructure.

Video: Reportage of the Stonehaven rail crash

A Network Rail spokesperson said: “We will be investing over £4bn in Scotland Railway over the next five years and running a safe and reliable service for our customers is our top priority.

“All of our plans for the future are agreed in advance with our independent regulator – the ORR – and will not compromise the safety of our railway or our people.

“We will be investing more money in drainage systems, earthworks and structures over the next five years and hiring additional frontline engineers.”