Bosses at Scottish Water have been accused of “behaving like Victorian mill owners” as a third union voted for strike action.

A ballot of Unison members at the publicly owned utility found almost four fifths (78%) were in favour.

Just over 70% of members took part in the ballot – making the union the third to return a result in favour of strike action at Scottish Water, after the GMB and Unite announced similar ballots.

The unions, meanwhile, have accused the utility firm of acting like a “rogue employer” after 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.

The row comes in the wake of Alex Plant, the new chief executive of Scottish Water, coming under fire for earning a reported annual salary of £295,000 in breach of the Scottish Government’s public sector pay rules.

Mr Plant’s salary is £25,000 higher than his direct predecessor despite the pay policy expecting a 10% reduction in the remuneration package.

Speaking after their ballot result was announced, Unison regional organiser Emma Phillips said: “It seems that the Scottish Government’s fair work and equality commitments don’t matter in our biggest and most precious public asset.

“There is a feeling amongst members that Scottish Water bosses are behaving like Victorian Mill owners – and this overwhelming vote for strike action is a reflection of how staff feel they are being treated.”

The key workers at Scottish Water need their overdue cost-of-living pay rise now

Ms Phillips said while there had been a meeting with the conciliation service Acas at the start of this week, “no positive progress” was made.

But she said the union was “committed to resolving this dispute” with a further “make or break” meeting due to take place early next week.

She added: “Unison and the other unions want to negotiate a new pay and grading structure with Scottish Water, but this is a complex process that relies on accurate data.

“It is not going to be resolved quickly and these discussions need to be separated from any cost of living pay offer.

“The key workers at Scottish Water need their overdue, cost-of-living pay rise now.”

We continue to seek to negotiate a resolution to this dispute over what we consider a very fair and reasonable proposal

A Scottish Water spokesperson said: “We are extremely disappointed that the unions chose to ballot their members on industrial action whilst we remain in talks with them, supported by Acas.

“We continue to seek to negotiate a resolution to this dispute over what we consider a very fair and reasonable proposal.

“It would increase the pay of every employee by at least 8% and transform our pay and grading structure, ensuring it is fit for the future. It has been developed specifically in response to the concerns our people have with our existing approach, which is now 20 years old.

“All our employees make a valuable contribution to the delivery of vital public water and waste water services for customers – their work underpins the daily lives of more than five million people.

“When their strong feedback suggested that the current pay and grading structure is outdated and requires modernisation, we listened.”

The spokesperson added: “Both sides will continue conciliation talks on Monday to seek to achieve an outcome that benefits all our employees.”