Hundreds of trains services have been cancelled or curtailed this week due to driver shortages linked to a bitter pay dispute ahead of a possible summer of discontent on the newly-nationalised Scots rail network.

On Thursday it is estimated there were over 100 service cancellations spread across Scotland including the key Glasgow to Edinburgh service and the world-renowned West Highland Line because of a driver shortage.

Over 60 further services had train carriages cut so they carried less people, because of the shortage.

Some customers were told by ScotRail on social media that the shortages were the result of "driver strikes".

There are concerns that Scotland is seeing the start of a summer of disruption hitting ScotRail and cross-border services through a series of pay disputes.

Cross-border services run by rail operator TransPennine Express (TPE) face a new round of disruption over the next four weekends as the Rail, Transport and Maritime (RMT) union escalates strike action over pay.

Thousands of Network Rail railway workers are also currently being balloted for strike action which it is feared will bring Scottish services to a standstill, as safety concerns surface over plans to cut hundreds of critical maintenance jobs.

The latest spate of cancellations comes as ScotRail launched a half-price rail fare offer this week to try and entice people back onto trains in the wake of Covid pandemic restrictions being lifted.

READ MORE:Anger as ScotRail plans cuts to services under state-ownership

It had been thought that the latest ScotRail disruption would be restricted to Sundays as the rail operator had been relying on overtime working on that day to train new drivers but had been hit by a lack of staff.

On Sunday, driver shortages were estimated to have hit 110 services across Scotland.

And on Monday, it was estimated 90 journeys had been cancelled

State-controlled ScotRail blamed disruption on Sunday on actions linked to a drivers' pay dispute.

It said said a significant number of drivers had stopped making themselves available for overtime and rest day working.

But it has been confirmed that there has was further chaos on the railway network yesterday because of a shortage of train drivers.

To cope with cancellations between Glasgow Queen Street and Fort William, Mallaig and Oban, ScotRail have been trying to bring in replacement buses but have had issues sourcing enough.

Rail tickets were to be accepted on local bus routes with CityLink between Queen St and Oban and between Queen St and Fort William, but admitted that "acceptance is very limited".

The train operator issued advice that "due to very limited replacement transport being secured, passengers are advised to consider making their own alternative arrangements".

Train drivers union Aslef has denied there has been any unofficial action as it prepares for a strike ballot over pay and after state-controlled ScotRail indicated at the weekend that there would be a driver shortage that would impact services.

Union sources have said that the system has always been "understaffed" meaning that drivers can take Sundays off to spend with their families as they are run on a six-day a week basis not seven.

Services rely on drivers to work not only contractual and overtime but extra Sundays and work on rest days to keep the railways running. Aslef sources say that if drivers individually chose not to work overtime, then the service cannot meet the seven day demand.

Jim Baxter, Aslef executive committee member for Scotland, has said that jobs that did not have drivers booked for them, due to holidays or sickness, were not covered as no one else was available to work them.

An Aslef spokesman said: "The lack of drivers is down to poor and successive failures by those who run Scotland’s railways. The Scottish people deserve better. We need a fully funded and staffed railway without the need to force staff to work overtime to keep the railway running."

The National Union of Rail, Maritime and Transport Workers (RMT) has said that its dispute with Network Rail will in itself be the biggest rail strike in modern history.

The union says Network Rail is planning to cut at least 2,500 safety-critical maintenance jobs as part of a £2 billion reduction in spending, including hundreds north of the border. Meanwhile workers have been subject to pay freezes and changes to their terms and conditions.

Strike action could begin in June if workers vote to walkout in the ballot which is due to close on May 24.

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That strike would not just hit cross-border services but the running of operations across Scotland, including ScotRail and Caledonian Sleeper services.

That is because among those being balloted are safety-critical workers including signallers employed by Network Rail who are crucial to keep trains running.

The Rail Delivery Group has said any strike would put at risk the post-Covid recovery.

Meanwhile, TransPennine Express recommended that rail users avoid travelling this Sunday and make their journey on either Saturday or Monday instead as only as "small number" of trains will be running due to the RMT dispute.

READ MORE: 'National embarrassment': More complaints over ScotRail disruption four months after winter timetable chaos

Further stoppages are expected on May 22, May 29 and June 4 and 5.

Disruption is also to be felt Network Rail, the nationalised body that owns and manages the infrastructure, such as the tracks and the signals, carries out engineering work between Carlisle and Edinburgh and Glasgow on Saturday and Sunday, with a replacement bus service running between Carlisle, Lockerbie, Edinburgh and Glasgow.

Aslef's national executive confirmed on Wednesday that it had made the decision to ballot members within ScotRail after the company failed to make a meaningful pay offer.

The union has said it has no option but to ballot for strike action after receiving a 2.2% pay rise.

ScotRail said that the 2.2% offer for 2022/23 came after three increases in pay between 2019 and 2020.

The Aslef ballot has come just over a month after the rail operator was taken into public ownership for the first time in 25 years.

The Scottish Government announced decided last year to take ScotRail under direct state control from April 1, stripping Dutch state transport firm Abellio of the franchise three years early in the wake of continuing outcry over service failings and rising costs to the taxpayer

It came after a 2018 winter timetable with the introduction of high-speed trains and new class 385 electric trains ushered in months of cancellations and disruption to services with much of it put down to staff shortages partly due to training to deal with the new trains and timetable.

ScotRail was forced to submit a plan by February, 2019, to address falling performance levels which, if unsuccessful, could result in a breach of contract and lead to Abellio losing the franchise early.

Aslef Scottish organiser, Kevin Lindsay, said there had been hope that the change of ownership may spark a “new era of positive industrial relations”.

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But he said: “We are beyond disappointed by the lack of action and any meaningful pay offer from ScotRail.

“Just a few weeks ago, we were celebrating our trains being taken back into public ownership, we hoped this would herald a new era of positive industrial relations, but it appears the same senior managers are determined to resort back to the failed strategies of the past.

“Aslef is committed to, and available for, talks at any time to help solve this impasse.”

Transport Scotland has said Sunday services were an operational issue for ScotRail and that the transport minister Jenny Gilruth understood the need from unions to negotiate a fair settlement for their members.

"Rail unions are aware any additional increase above public sector pay policy amounts have a clear process which must be followed which includes Cabinet approval," the spokesman said.

READ MORE: ScotRail apologise over 'shambles' introduction of new winter timetable

"Noting that all ScotRail employees have already received the previously negotiated and agreed 2.2% increase for this year, we would encourage them to continue meaningful dialogue with ScotRail so a mutually agreeable outcome can be reached as soon as possible.

"It is our intention for ScotRail and its staff to benefit from the transition to public sector control and that is why we would call on everyone involved to take time to consider all options carefully."

David Simpson, ScotRail service delivery director, said: “It is very disappointing that we find ourselves at this stage with ASLEF, despite a very good offer being made. We have made a pay offer that recognises the hard work of our colleagues and the cost-of-living challenges faced by families across the country, while delivering value for the taxpayer.

“We are still trying to recover from the pandemic. With customer numbers around one third below pre-COVID levels, it remains a very challenging time for Scotland’s Railway.

“We have assured ASLEF and our workforce that we remain open and committed to further discussions to resolve the dispute and move forward together to provide the safest, greenest, and most reliable railway we can for Scotland. I ask union members to vote no so we can focus on that recovery.”