Firms involved include Hochtief, VolkerFitzpatrick and Graham
Pictures have revealed the progress being made at the stations being upgraded at the eastern and western ends of Crossrail.
Network Rail is responsible for station enhancement works for the Elizabeth line on the branches running out to Shenfield in the east and Reading and Heathrow in the west.
In the west, works are progressing at Acton Main Line, West Ealing, Ealing Broadway and Hayes & Harlington stations.
Graham will be in charge of improvement works at Acton, West Ealing and Ealing Broadway.
Hochtief is behind work at both Southall and Hayes and Harlington stations, as well as carrying out major refurbishment works at West Drayton station.
In the east, VolkerFitzpatrick has started works for major station enhancements at Ilford and Romford in Essex.
Last month, Network Rail confirmed it would need an extra £140m to finish the work for Crossrail.
It said the additional costs for the Network Rail surface works package were assessed before the covid-19 pandemic and were the result of “station and power upgrade work taking longer than planned”.