Both tracks were blocked by the incident, in which an East Coast train lost its pantograph - which connects the locomotive to the wires - with the downed cables stretching behind it.
Diesel trains on the line, such as East Coast services between Aberdeen, Inverness and London, were diverted onto another line to bypass the blockage, adding one hour to journeys.
However, electric trains, including most Edinburgh-London services, were being held up, with only a few able to get through by being hauled by diesel locomotives over the diversionary line.
Passengers said a train guard had told them the fault was “very serious” and trains were stuck all the way from Edinburgh to Newark in Lincolnshire
Travellers delayed included large numbers of people returning from the Edinburgh Festival.
The incident comes after the latest figures showed East Coast was Britain’s least punctual train operator in the four weeks to 17 August, with 85.7 per cent of services arriving within ten minutes of schedule compared to 89.1 per cent a year ago.
In addition, only 57.9 per cent of its trains arrived within one minute of time over the previous year.
However, Network Rail was responsible for 69 per cent of delays over the previous month, which included lightning strikes hitting signalling in the Borders and a cow hitting a train near Doncaster. A train also broke down near Grantham.
CrossCountry, which also runs cross-Border trains on the east coast line, had the worst “right time” performance, with 45.2 per cent of services on time.
Virgin Trains, which operates Scotland-London services on the west coast line, was on 47.4 per cent, while ScotRail’s figure was 58.1 per cent. First Transpennine Express, which also runs cross-Border trains on the west coast line, was at 61.9 per cent.