Lack of training and guidance for those investigating workplace accidents means that companies responsible for the deaths of workers and the public will still not be brought to book, according to Thompsons, the UK's leading trade union law firm, and train drivers' union ASLEF.

While welcoming the addition of the British Transport Police and Local Government Association to the signatories to the protocol, Thompsons and ASLEF warn that the protocol will not prevent a disaster in future because the police are still ill-equipped to investigate workplace deaths.

Thompsons, ASLEF and the Fire Brigades' Union, in a joint submission to the HSE last year, called for a thorough overhaul of the way workplace accidents are investigated, focusing on the role of the police and whether they have sufficient training and understanding of work-related deaths.

The police, HSE and CPS should be fully trained in the relevant law and how to investigate this sort of death and all investigations should be done jointly by the police and the HSE. Detailed guidance needs to accompany the protocol.

Call for a specialist unit to investigate work related deaths

Thompsons and the trades unions also called for a specialist unit to investigate work related death incidents.

Michael Appleby, head of health and safety at Thompsons said: "Proving manslaughter or corporate manslaughter is difficult enough, but the problem is compounded if there has not been a satisfactory investigation. We welcome the fact that the revised protocol places the emphasis on a manslaughter investigation. But if the officer has never investigated a work-related death and doesn't understand the industry how will he / she know? How will he / she know what evidence should be preserved and recovered straight away? Unlike Sir David Calvert-Smith QC, I am not assured that prosecutions resulting from workplace deaths will be based on the best evidence."

But no amount of training or revisions to the protocol will address the underlying reasons why investigations fail to prevent accidents happening again, ASLEF says.

Mick Rix, ASLEF general secretary, said: "Accidents and disasters within the rail industry are caused by the lack of funding of the industry and the lack of a national railway strategy. There are a myriad of agencies already involved in investigating rail accidents, from the police to the train operating companies, the infrastructure companies and the maintenance firms. They are not sufficiently focussed on coming at the investigation from the point of view of there having been a failure by companies to protect the lives of workers and the public. Although we welcome the inclusion of the BTP - something that is long overdue - we fear it cannot save lives and make workplaces safer in the future."