The incident happened when three Victoria Line trains were stopped in a tunnel outside Highbury and Islington station, north London, on a very hot summer's day in July 2001.

Passengers were stuck on the packed trains for 90 minutes in sweltering conditions.

About 600 people had to be treated for heat problems, with 18 so badly affected they had to be taken to hospital.

HOW THE CRISIS UNFOLDED

Three trains trapped on a hot day 600 passengers treated for heat problems 18 taken to hospital The management of the crisis was poor, said LU The incident was "distressing" and a "near-miss", said its report

An internal report by London Underground (LU), seen by Radio 4's Today programme, said the incident was so badly handled, the outcome could have been even worse.

Passenger Jason Groves was trapped for 85 minutes. He told Today: "The Tube was packed, I was stood up between the seats.

"We'd keep getting announcements every 10 minutes or so, but you were getting the impression the driver doesn't actually know what's going on.

"It was just getting hotter and hotter and hotter. People were starting to rip the advertising boards off above the seats, and try to use them as fans, but you were packed so tight, you couldn't really do that.

'Disastrous' consequences

"There was a pregnant woman collapsed... everyone was crying out for water but you don't take much water in with you if you're just going to work."

The incident, which the LU report described as "an example of the near-miss principle", began after a train stalled following a problem with a sliding door.

People were starting to rip the advertising boards off above the seats, and try to use them as fans, but you were packed so tight, you couldn't really do that Passenger Jason Groves

"There were a number of times when, had conditions been very slightly different, the consequences could have been disastrous," said the LU report.

"There was a very slow realisation, especially on the part of the control room, to accept the seriousness of the situation on the ground."

Radios were not working and there was a lack of communication between staff, it added. Decisions kept being passed up, delaying any action being taken.

One train driver did not know people were being taken off his train and could have moved off, risking passengers or staff falling onto the live track, the report said.

No plans for improvement

Tube trains create their own "forced air" ventilation with their movement and once they stop there is no new ventilation for passengers.

The report called for previous initiatives to address the ventilation problem to be "supported and accelerated".

HOW THE CRISIS UNFOLDED

The chain of command didn't operate as it should have done Mike Shrelecki, London Underground

However, there are no provision in the public-private partnership plans, which should bring �16bn of investment to the Tube, to improve air ventilation on the deep lines.

Mike Shrelecki, director of safety for London Underground, told Today that engineers were trying to find technical solutions to the "challenge" of improving the Victoria line, but so far this had proved "physically impossible".

He said several changes had nonetheless been made which should prevent such an incident happening again.

"We've changed the standards for command and control during incidents, and duty managers and controllers have been trained in those new standards," he said.