This picture, taken by passenger Martin Stewart, shows the broken cable hanging over the track in Radlett station yesterday.
Severe delays have been predicted on Southeastern, East Midlands Trains and First Capital Connect until the end of the week.
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The venue says it is in contact with promoters about a final decision, following the terror attack at the singer's concert on Monday.
Soldiers will replace armed police at many sites after security experts warned the Government that another terrorist attack may be imminent.
The threat level has been raised to critical by MI5's Counter-Terrorism Analysis Centre.