In the early 1970s , fifty were fitted with electric train supply in place of their steam-heating boilers and assigned to work services on the Midland Main Line from London St Pancras to Nottingham , Derby and Sheffield .
In the early 1970s fifty were fitted with electric train supply in place of their steam heating boilers , and assigned to work services on the Midland Main Line from London St Pancras to Nottingham , Derby and Sheffield .