The Metropolitan Railway did not suffer the same size constraints as the 'deep tube' lines and electric Locomotives were a powerful alternative to steam.
During 1922/23 a new set of electric locomotives, built by Metropolitan Vickers Ltd. at Barrow-in-Furness entered service utilising the former steam-hauled carriages.
Each locomotive weighed 61.5 tons, were 39ft. 6ins. long, and were capable of accelerating from rest to 25mph in 25 seconds with a top speed of 65mph. They were also designed to start a 265 ton freight train up a 1 in 45 gradient on a straight track and could shunt at speeds as low as 2mph
'Sarah Siddons' is the ex Metropolitan Line Bo-Bo Electric Locomotive Number 12. It is maintained in working order and makes occasional forays onto the London Underground network for special events such as the sadly now defunct 'Steam on the Met'.