The concerns of the Health and Safety Executive came to light in a letter to Railtrack from the deputy inspector of railways, Vic Coleman.
That said prosecutions of Railtrack by the HSE were being considered. In two cases, Mr Coleman wrote, track was "in such an extremely bad condition so as to be unsafe".
Railtrack already faces an HSE prosecution over a freight train crash at Bexley in Kent in February last year when seven wagons left the track, injuring four members of the public.
The inspectorate remained "concerned about the condition of track on the Railtrack network".
In one incident highlighted, a passenger train left the rails at Harwich, injuring a passenger. Two days later, a nuclear waste train was derailed a mile along the same line.
Mr Coleman said his inspectorate would not tolerate track that was "not being maintained in a condition so as to reduce the risk of railway passengers and employees so far as is reasonably practicable".
Railtrack said it had met safety inspectors last week. "The railway is safe and this remains a Railtrack priority," a spokesman said.
The company's critics say it is parsimonious. "Railtrack has underspent its maintenance budget by pounds 277m, so a less safe railway is an understandable result," said Jonathan Bray of Save Our Railways.
Safety is a key concern for Railtrack. It had a setback in 1994, when it took over from British Rail. Then empty passenger coaches were derailed on tracks approaching Euston station, London. The HSE then issued an enforcement notice making the company replace worn-out tracks.Reuse content