An exam marking boycott by lecturers could have a "catastrophic" effect on Summer graduations at one of Scotland's oldest universities, union leaders have warned.

The University and College Union (UCU) says there is a risk degrees will be "undermined" at the University of Glasgow if a long-running, national dispute over pay and conditions is not settled.

Edinburgh University has said it is going to graduate students with unmarked work while Glasgow is outsourcing marking.

Exam invigilation is also affected as well as "quality assurance" on degrees such as second marking, moderation and external examiners.

The UCU and members of the EIS-Further Education Lecturers’ Association (EIS-Fela) are taking action short of a strike in an attempt to secure higher wages.

The University of Glasgow said it was working with schools to ensure that "no student is prevented from graduating, because of the industrial action.”

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"Glasgow's mitigation strategy has been that they will find new markers," said Kirsteen Paton, a sociology lecturer and Glasgow rep for the UCU.

"I can't tell you how impossible that is going to be so I don't know if they are naive or in denial about the scale of things.

"Because of workloads and growing student numbers, the turnaround to get student marks back in time for exam boards and graduations in the Summer is already completely pressurised.

"We struggle to do it under normal conditions. There is no way the current graduation schedule is going to happen.

"The concerns are that it will be people with no knowledge or experience of that topic or course.

"It could be inexperienced markers - I think they have been targeting PHD students."

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She said there was now a "slow realisation" by students that coursework such as dissertations was not being marked.

She said: "I think it's going to have a catastrophic impact on graduations.

"There are some areas that are 100% unionised so I don't know where they are going to find those markers."

The union is planning an open meeting for students next week who are concerned about their degree.

"Students should be alarmed and students should be angry," she said.

Staff say they have experienced a 25% pay cut in real terms since 2009 while there around 100,000 university workers are on casual contracts.

"Some of the people doing the marking boycott don't even have jobs at the end of the month, that's what is at stake for them," said the union rep.

"There is a simple way to resolve this - to get back round the table. What they are willing to do instead, is sacrifice the quality of degrees."

A University spokesperson said: “We regret the UCU is taking industrial action, but the large majority of staff continue to work normally and the University is doing everything to keep disruption to students to a minimum.

"The University will continue to work with all Schools, seeking to ensure that no student is prevented from progressing to the next stage of their degree, or graduating, because of the industrial action.”