Tens of thousands of tube commuters are paying the price tonight for an extraordinary blunder by workmen.
A key section of the Victoria Line is at a standstill after crucial signal equipment was swamped by liquid concrete.
The accident involved contractors working on the £695m project to expand Victoria Underground station.
Concrete being used to reinforce new excavations flooded a signal room. Underground bosses say human error was to blame.
Engineers are now in a race against time to try to remove the concrete before it sets.
The Victoria Line - which carries 500,000 passengers a day, was suspended between Warren Street and Brixton shortly before this evening's rush hour.
The line is unlikely to re-open tonight and services may still be at a standstill tomorrow morning.
Read more: London Underground's response here