The Victoria line will become the first cooled section of the Tube network under plans to revamp ventilation shafts along the route.
Works will be carried out in two phases worth more than £25 million each and will involve installing upgraded fans at mid tunnel ventilation shafts dotted along the line.
A contractor source said: “Originally a tender document was due this month but we now expect to see it around April. The line is one of the deepest on the underground and probably the one that needs cooling the most. Hopefully it will be done for the Olympics in 2012.”
The scheme is currently being designed to RIBA stage D, which is drawn up before a project is submitted for planning.
Once complete, London Underground will look to external suppliers for fans. The first phase of the project will see upgrades at six shafts with a further 10 scheduled for the second phase. Work should start five months after a tender is issued.
Several contractors are already expressing interest in the works with Costain and Taylor Woodrow set to bid.
Above ground, competition for the £400 million Victoria Station refurbishment is also hotting up with five firms set to bid for the works.
Costain, Taylor Woodrow, Sir Robert McAlpine and a joint venture of Balfour Beatty and Morgan Est all expect to return tenders to Network Rail in 10 days’ time.
Works on the station, which serves local south London commuter routes as well as longer journeys to the Kent, Sussex and Hampshire coasts, will include a new subsurface northern ticket hall, extensions to the existing subsurface southern ticket hall, new tunnels to provide more access to existing platforms and sewer strengthening works.
Step-free access to the Victoria, Circle and District lines is also part of the project and will be achieved through the installation of new escalators and lifts.
The station is used by 75 million passengers a year and the upgrade will increase the size of the station by about 50 per cent. Construction will begin in 2009 and is scheduled to finish in 2014.