New evidence that hundreds of seals have been slashed to death and beheaded by a type of propeller used in shipping and offshore industries has prompted a powerful plea for a worldwide ban.

A scientific study for the Scottish Government by the Sea Mammal Research Unit at St Andrews University has confirmed that seals trapped in ducted propellers suffer horrific and fatal "corkscrew" gashes. The reports suggests larger seals could be decapitated by the blades.

Ducted propellers run inside a casing, which makes them more efficient at low speeds, but it is thought the animals get trapped between the propeller blades and the casing.

Angered by the deaths, a coalition of 26 wildlife and conservation groups is now demanding a Scottish, UK and international ban on the guilty propellers. They have written to the Scottish and UK governments warning that they are breaking the law by failing to protect seals.

"This is one of the UK's biggest marine conservation and welfare tragedies," said Sarah Dolman, Northeast Atlantic programme manager for Whale and Dolphin Conservation, the group that co-ordinated the joint letter.

"This latest evidence confirms that seals are being sliced up by some kinds of ships' propellers and possibly in much greater numbers than previously realised. Despite the worst-affected populations of harbour seals heading for local extinction, we have not seen any evidence that the UK and devolved governments plan to act to stop these needless deaths."

About 100 seals have been officially confirmed killed in Scotland by what scientists describe as a "single continuous curvilinear skin laceration spiralling down the body", most of them since 2010. But this relies on carcasses being washed ashore and reported, so it is very likely to be a "gross underestimate", the new study says.

It also points out that reports of adult grey seals found beheaded are "common in the UK". The possibility that they have lost their heads to covered propellers because they are larger than other seals killed by corkscrew injuries needs to be investigated, the study says.

The study concludes that under its testing conditions, "ducted propulsion systems were the only mechanism which produced spiral lacerations" and says further research is needed to understand how the injuries occur before anything can be done to stop them.

But this is rejected by wildlife groups, which argue it is time for action. "There is already ample evidence that ducted propulsion systems are responsible for these gruesome injuries to huge numbers of seals," said Dr Richard Luxmoore, senior nature conservation adviser to the National Trust for Scotland. "Exclusion devices are already being used in other parts of the world to prevent them and it's time we made them compulsory here. The rush for offshore wind farms is partially to blame but we don't want them built on foundations spattered with seal blood."

Conservationists are particularly worried that four large new wind farms were given the go-ahead last month off the Forth and the Tay without restrictions on the types of propellers that could be used on the vessels which service them.

Seal numbers in the area have been plummeting, partly due to corkscrew injuries.

Environmental lawyers say there would be a strong case against the UK Government if it failed to take action. "The UK has legal duties to protect seals," said Sarah Gregerson, from the green law group ClientEarth. "Immediate and simple measures can be put in place by authorities to prevent these injuries."

Scottish Renewables, which represents wind-farm firms, argued offshore wind was a new industry and so could not be blamed for past injuries. Developers were required to mitigate and minimise disturbance to marine mammals at all times, it said.

The shipping industry opposed a propeller ban, and complained it had experienced difficulties engaging with researchers on the issue. The UK Chamber of Shipping is due to meet with the Government's Marine Scotland on November 12.

"The death of any sentient marine mammal, particularly after sustaining such horrific injuries, is something that no mariner would wish to see happen," said the Chamber's policy director, David Balston.

"Once the cause of these injuries is fully understood then steps can and should be taken as a matter of urgency to prevent more incidents. A blanket ban in the interim, however, is neither realistic nor sensible."

The UK Government said it would consider the new study's findings. The Scottish Government stressed it was funding the world's only research into corkscrew injuries, which have been seen in nine other countries.

"Good progress is being made narrowing down the cause of these deaths, but we do not yet have conclusive results," said a spokeswoman. Results "will inform whether Scottish, UK or international action might be most appropriate."