Hundreds of staff at the nation's state-owned water supplier which has been at the centre of a row over executive pay are set to strike in December amid claims the organisation attempted to force through changes to pay and conditions without agreement.

Last-ditch talks are expected today through the conciliation service Acas to avert the first strike at Scotland’s publicly-owned water company.

But some union insiders say there is no great optimism of a resolution, saying it appeared to be a 'tick box' exercise.

The results of official ballots are expected over the next few days with the GMB union saying it is expected they will support strike action.

Scottish Water would be given two weeks notice of strike dates - meaning the stoppages could take place in the start of December.

GMB says 83% of its members are in favour of taking industrial action amid the dispute according to a consultative ballot.

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Unison which has consulted members on taking industrial action has found 82% are willing to do so unless proposed changes to their pay and grading are withdrawn and a better salary offer is put forward.

Unite held a consultative ballot among its members at the firm and found 92% are willing to walk out, a figure the union says means around 500 staff are prepared to strike.

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Scottish Water say that their offer is "fair and reasonable" and would mean an 8% rise in pay for every staff member alongside a pay and grading structure reform.

But unions say the pay needs to be split from the reform which they believe will have long-term impact on workers’ pay and should be subject to separate negotiations.

The development comes amidst concern from unions that Alex Plant, the new chief executive of Scottish Water, is being paid £295,000 a year – a salary that is £22,500 higher than his predecessor and £50,000 above the expectation in the Scottish Government’s public sector pay rules.

The Scottish Government's pay policy published in March stated a continuing "expectation" that there should be a 10% cut for all new chief executives.

But the Scottish Government has insisted that in this instance there was no breach of the rules.

A Scottish Government spokesman, in saying there was no breach, referred to pay policy guidance which has been in place since 2010 and is updated annually, saying the expectation of a reduction in a new chief executive's pay was predicated on the ability to fill the post with a suitable candidate having regard to external market levels, value for money and recruitment and retention issues.

The Scottish Government had previously declined to explain how the caveat relates directly to the appointment of the Scottish Water chief executive.

The row led to calls that there should be a rethink on public pay with GMB Scotland saying the guidance "demolished" the credibility of the rules and that unions should be fully consulted on them in future.

The Herald: Alex Plant, director of strategy and regulation for Anglian WaterAlex Plant

Scottish Water, which is responsible for the public water supply and waste water services of five million people and directly employs nearly 4,500 people has previously stated that the chief executive's salary was "less than any comparable water company chief executive in Great Britain".

Claire Greer, GMB Scotland organiser, said the Acas talks were likely the last chance for management to avert a strike after unilaterally linking a pay offer to a new grading structure.

She said: “We sit in meetings and managers to ask what they can do to sort this out.

“We tell them, they nod their heads and then carry on regardless."

The unions, who will join the Acas discussions on Monday afternoon are in formal dispute with Scottish Water claiming managers sent an email to all staff detailing the proposed structure without consultation or agreement.

The union has accused the publicly-owned firm of acting like a “rogue employer” by combining an annual pay offer with a restructuring of salaries and grades, which, they say, will limit the wages of many lower-paid workers in the years ahead.

“What they need to do to sort this out is to decouple this year’s pay offer from the far wider review of the salary structure and discuss and agree each of them separately," said Ms Greer.

“Executives at Scottish Water seem to believe negotiation can take place when there is no one in the room but themselves. It doesn’t work like that.

“This dispute has been needlessly created by management riding roughshod over every accepted procedure for negotiating with staff.

“They have been told this repeatedly but, after ignoring every one of those warnings, they are running out of time to avert action.”

A Scottish Water spokesperson said: “We continue to seek negotiations with trade unions over what we consider to be a very fair and reasonable proposal. If agreed with our unions, this would increase every employee’s pay by at least 8% and reform our pay and grading structure in a way that our colleagues are asking us for.”

“We have jointly engaged ACAS, the conciliation service, and are due to meet next week to support what we hope is one of our shared objectives, which is to reach an agreement in the best interest of our people as soon as possible.”