Manslaughter charges will not be brought over the Potters Bar rail crash in which seven died and 76 were hurt, the Crown Prosecution Service has said.
Health and safety charges could now be brought
The CPS said there was not a "realistic prospect of conviction" of any individual or company for an offence of manslaughter by gross negligence.
The 2002 Hertfordshire crash was caused by a faulty set of points.
Relatives said they were angry but not surprised. The case will be referred to the Health and Safety Executive.
More than 70 people were also injured when a London to King's Lynn train derailed just before Potters Bar station on 10 May 2002.
The points at the time were operated by Railtrack - whose responsibilities were taken over by Network Rail - and maintained by engineering firm Jarvis.
Crucial nuts that should have been holding the tracks together were found lying unscrewed alongside the rails.
The British Transport Police have not been able to discover when the bolts came loose - and who might have been responsible for ensuring they were tightened.
In the most recent report into the crash, the Rail Safety and Standards Board (RSSB) said the cause may have been maintenance practices dating back to before privatisation.
The second report by the Health and Safety Executive in May 2003 found no evidence of sabotage or deliberate unauthorised interference with the points.
HSE investigators have now taken over to examine whether health and safety laws were broken.
The HSE said it would be awaiting the result of a coroner's inquest before deciding whether to bring any charges.
The practice is normal HSE policy and recognises the fact that additional information may come to light as a result of the inquest or the coroner may decide to refer the case back to the CPS.
Corporate killing laws
A relative of one of the victims said she was "angry and bitter but not surprised" at the announcement.
"It was quite obvious that this crash was due to bad maintenance," said Perdita Kark, whose father Austen Kark, 75, died.
"I don't want to see the chap who wielded the spanner take all the blame."
Police have not been able to discover how track bolts came loose
Ms Kark said the existing corporate manslaughter laws were "very problematical".
Her sentiments were echoed by Bob Crow, general secretary of the RMT union and Keith Norman, general secretary of the train drivers' union Aslef.
Mr Crow was among those calling for the proposed government overhaul of corporate manslaughter legislation to be brought in quickly after the Hatfield rail crash trial ended at the Old Bailey with convictions over health and safety breaches.
"Once again, justice has failed to be done because there is no proper corporate manslaughter law in place," he said.
Under existing law, a company can be convicted of corporate manslaughter only if a senior individual in that company is guilty of "gross negligence manslaughter".
Network Rail said it would continue to co-operate with the HSE.
"Over the last three years there have been many changes on the railways.
"Network Rail - a not-for-dividend company - took over from Railtrack in 2002.
"Maintenance has been taken in-house, restoring the link between ownership and upkeep of the rail infrastructure."