Transport and Olympics chiefs were left red-faced today as massive delays on their big test day placed a big question mark over the capital's readiness to cope with the Games.
Thousands of commuters hit trouble as the entire Docklands Light Railway - a key transport artery for the Games - was suspended after a "communications failure."
At the same time during the early morning rush hour a signalling problem struck London's Liverpool Street station, knocking out four platforms.
Journey times were extended by up to 20 minutes into and out of the station, one of the busiest in the country.
And London Overground services into the Olympic Park at Stratford were delayed by up to 25 minutes due to over-running engineering works.
Rail Maritime and Transport union general secretary Bob Crow said: "The widespread disruption following a series of infrastructure failures, shows just how the London transport system is hanging by a thread as the final countdown for the Olympics and Paralympics begins.
"Added to the train hitting a buckled wall just a few days ago we have seen the most graphic illustration yet that ahead of the biggest transport challenge London has ever faced we are out there on a wing and prayer."
The disruption coincided with the Olympic Park facing its biggest test to date as it began to host six events over seven days as part of the final preparations for the Games.
More than 140,000 spectators will watch 3,000 athletes take part in water polo, hockey, wheelchair tennis, athletics, paralympic athletics and boccia.
A nine-day exercise testing security and the military involving Royal Navy ships, RAF helicopters and jets also began today.
East Midlands Trains said a second strike by members of the drivers' union Aslef tomorrow in a dispute over pensions will lead to a revised timetable.
Further stoppages are planned on May 8, 10, 15 and 17. The first strike was on Tuesday.
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