The 34% under-reporting figure was confirmed in a report published today by the Rail Safety and Standards Board.

But the report cleared Network Rail bosses of claims that they encouraged under-reporting of accidents to protect their bonus payouts.

Network Rail is now vowing to improve its safety culture with the area “a the top of David Higgins’ in-tray” when he takes over as chief executive.

The report was commissioned by Network Rail last June following claims from the Unite union that managers were encouraging contractors not to report accidents which kept people off work for three days or more.

The 99 page report concluded that there has been a 34% under-reporting of ‘over-3-day injuries’ amongst staff and contractors since 2005.

Causes included misinterpretation of reporting requirements and fear felt by Network Rail staff and contractors if they reported accidents. The report said there was no link between under-reporting and executive bonuses.

Rick Haythornthwaite, Network Rail’s chairman, said: “While we can take some comfort from the report’s clear conclusion that there was no link between under-reporting and executive bonuses, Network Rail needs to heed the lessons in this report if it is to achieve its ambition of a world class safety culture.

“Enhancing safety, both at Network Rail and its contractors, will be at the top of David Higgins’ in-tray when he starts as chief executive. Under David’s leadership I am expecting the company to deliver a step change in safety.”

Peter Henderson, Network Rail’s acting chief executive, said: “Enhancing the safety of the railway and establishing a more open culture is a complex issue.

“To achieve our safety ambitions, we will work together with our contractors, unions and other stakeholders and use these findings to help develop a wide-ranging safety plan.”