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.
More top news
Detectives are linking three attacks on women in South London and are warning the level of violence has escalated with each attack.
Tube delays sparked by overcrowding have more than doubled since 2013, according to figures obtained by the Liberal Democrats.
Officials at Transport for London have said sorry after a bus driver left a disabled passenger stranded on the roadside.