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
London mayor Sadiq Khan is "extremely worried" about knife crime as the Met Police revealed there were 9,000 stabbings in the capital.
Camden police have responded to reports of an unexploded World War Two bomb in Hampstead high Street.
AFC Wimbledon face Plymouth in the League Two play-off final at Wembley, with a place in League One at stake.