The London Ambulance Service says it expects its 999-call computer system to be back up and running "in the next hour or two."
A spokesman said that the technical issue had been identified and that they were now bringing the system live again.
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The Hammers moved to the Olympic Stadium in May leaving their old site to be developed for housing.
The first officer shouted "look!" as the drone passed next to the right wing at around 11,000ft above south-east London.
They found a sheepish looking ewe with a traffic cone on her head in the middle of a field.