Today’s Evening Standard reports that an Iraqi national was discovered at 3am between Seven Sisters and Finsbury Park stations. The intruder had access to the running lines, signals and points.
The incident happened two weeks ago but only came to light after a confidential report was handed to the paper.
The incident will concern Londoners who have been told by Met Chiefs that a terror attack on the capital was "inevitable".
Experts have predicted that the tube system would be high on any terrorist ‘hit list’. Just one month ago security sources were claiming they had foiled a major chemical attack on the city.
Speaking to the Standard Bobby Law, London district secretary of the RMT Tube union, said: "Clearly nothing has been done (to improve security) since the Madrid bomb and nothing really has been done since 9/11."