A new investigation into the maintenance of the railways by Jarvis is under way after it failed to properly reassemble track, the BBC has learnt.
The Kings Cross derailment caused weeks of disruption
The company has suspended a member of staff after the problem was discovered near Alexandra Palace in north London.
Radio 4's You and Yours programme learned the tracks were cleared for trains to pass without being properly reassembled.
It happened on 6 October on the same stretch of track and less than a month after an accident in which an express train derailed at King's Cross station on points which had been repaired by Jarvis.
The company had been working on the line near Alexandra Palace and had told Network Rail that the work had been completed.
But the driver of the first train to approach it reported that the signals were not working properly.
When engineers from Network Rail carried out an inspection they found the fishplates, which join together one of the sections of rail, were missing.
Jarvis told the BBC in a statement that the automatic fail safe mechanisms built into the railway prevented any trains from running over the track and that a member of staff had been suspended following the incident.
Shortly after the Kings Cross derailment on 16 September, Jarvis announced they were pulling out of rail maintenance.
The company said a faulty set of points that had not been properly reset after overnight maintenance work was to blame.
Last week Network Rail announced it was taking all routine maintenance back in-house.
The Health and Safety Executive (HSE) told the BBC that this incident was being investigated by the same team which is looking at the Kings Cross derailment.