Jarvis revealed last week that it may sell half of its stake in Tube Lines, the firm responsible for upgrading one-third of the London Underground, to reduce debt.
The PFI provider stressed that any deal would take "months" to conclude and was in its "very earliest stages".

In a statement the firm said: "With the joint venture having been operational for well over a year, the company believes it is the appropriate time to consider this move."

The information is to be revealed in documentation that will be published for a refinancing of debt that supports the Tube privatisation deal.

The deal is for the Tube Lines consortium, which was set up in 2002 and has responsibility for the Piccadilly, Jubilee and Northern lines. Jarvis owns one-third of the group alongside American construction group Bechtel and Amey.

The refinancing will mean that about £30m will go straight into the hands of the private sector when the £2bn debt changes hands.