"We understand that a foot of concrete burst into the control room having been poured into an escalator void.
We await further information but what we do know is that LU technicians are on site now working flat out to clear up the mess and get services back on line, proving once again that its directly employed public sector staff who are needed to deal with this kind of emergency, making a nonsense of Boris Johnson's tube staff cuts plans."
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John Cantlie, who worked for a number of Fleet Street newspapers, is thought to have been taken hostage in November 2012.
The union published a 'no show' league table for last year the worst offenders for cancellations.
Zalkalns was jailed in his native Latvia for eight years in 1988 after he admitted killing his wife with a piece of electrical equipment.