P&O plans to double the time crew members spend aboard cross-Channel ferries could increase stress and fatigue and compromise safety, according to the author of a report that warned of the dangers of extending tours of duty.

Having sacked almost 800 workers without notice earlier this month, P&O plans to extend the tour of duty of marine crew – workers on deck managing the ship – from one-week on, one-week off to a 15-day shift pattern. Sources suggest customer services staff will move to an eight-week model.

Chief executive Peter Hebblethwaite told Scottish MPs this week that the new crewing model would help cut costs without compromising safety.

But Professor Andrew Smith, an occupational health psychologist who conducted research commissioned by P&O on its cross-Channel ferries, told Sky News extending shift patterns was not supported by his findings.

“We found that crews on the Dover-Calais routes experienced very high levels of stress and fatigue that potentially could have compromised safety. Not surprisingly, when you are in that situation you want to minimise tours of duty,” he said.

“Extending from the current one week patterns to two weeks would not be recommended on the basis of what we saw.”

Professor Smith was commissioned in 2012 to conduct research into P&O when the company, then already owned by DP World, was considering extending tours of duty from a one-week pattern to two-weeks on, two-weeks off.

He surveyed almost 500 seafarers on the Dover-Calais route and 50 crew on the Larne-Cairnryan crossings, which then and now worked on a two-week pattern.

He found fatigue was significantly higher on the more intense cross-Channel routes.

“The number of crossings, the speed of port turnarounds, traffic in the Channel and lack of sleep all lead to a strong potential for fatigue,” he wrote in his final report.

Having reviewed the report a decade on, Professor Smith told Sky News he stood by its findings.

“The English Channel is described as the M25 of shipping, and we found there was more fatigue on these routes because they’re so busy, the crossing is very quick, the turnarounds are fast and intense,” he said.

“It’s not like the Irish Sea routes where there is less traffic, or they travel overnight so there is opportunity for rest. The plain sailing is not the problem, it is the port operations, the turnarounds, getting the cars and freight on and off so rapidly that contributes.

“I spent time on deck and saw how attention to health and safety could be compromised by commercial imperatives. For example, I was impressed that there were lookouts on the bridge watching for other vessels during crossings.

“But on the harbour approach, when they were arguably most needed, they were also responsible for getting cars off.”

Professor Smith made a series of recommendations, including conducting staff surveys regularly, making fatigue awareness part of health and safety training, and a detailed audit of safety-critical tasks such as watch-keeping.

Once he submitted his report however, he did not hear back. “I put forward some recommendations and they didn’t ask me to come back.”

Both P&O’s competitors on the Dover-Calais route, DFDS and Irish Ferries, work to two-week shift patterns.

Mr Hebblethwaite told SMPs that he was imposing a “fundamentally different operating model” that would cut the number of full-time crews from four to two, who would only be paid for when they are working.

“This is an absolutely safe model, it’s a model that is used in 80% of shipping around the globe, we recognise the intensity of each of our routes and we will put in place appropriate rosters,” he said.

“This is about moving to a competitive model, not undercutting other operators, and I assure you it’s safe, and I assure you no ships will be going to sea that are not safe.”

The Marine and Coastguard Agency has detained two P&O vessels, including the Price of Kent operating from Dover, after new crews made up largely of agency staff failed initial safety inspections.

Inspections of another Dover-Calais ferry the Price of Canterbury is understood to have been delayed.

Mick Lynch, secretary general of the Rail and Maritime Union, said: “The low-cost crewing models P&O want to bulldoze through come at a high cost of staff welfare and passenger safety. We have warned repeatedly that the whole attitude of the company revolves around winging it on safety to pump up profits.”

“The stress impact on staff comes with potentially lethal consequences and has to be taken seriously by the Government and their agencies.”