Tube Lines said "To reach many parts of the station like the sides of escalators, pipes and high up empty spaces, specially-qualified cleaners must abseil when the station is closed to passengers.
Every year for eight to ten weeks, a team of about four abseilers works its way around Westminster station to clean remote areas and change all the light bulbs. Tube Lines, which is responsible for maintaining the Jubilee line, works with CCS Jeweltone to complete this work."
There are more striking, photos of Tube cleaners or Fluffers in a post earlier this year, and they seem to have had a less scary looking task.
I'm assuming Tube Lines may have also employed an abseiling photographer with a good head for heights to take the pictures above!