Six people have been arrested after the theft of cable from a rail project being carried out by Atkins, it is understood.
Between £200,000 and £300,000 worth of cable has been stolen from the Basingstoke resignalling project during the past year.
Network Rail said thefts were symptomatic of a widespread problem, driven by the high value of the scrap metal industry.
There were more than 1,000 incidents of cable theft in 2006/07.
Network Rail said it is taking steps to prevent theft by working with British Transport Police, using security patrols, CCTV, a helicopter and by marking cables.
A Network Rail spokesperson said: “These thefts cause massive disruption for rail passengers.”
Cable on the Basingstoke project has been stole from sub-stations and depots, which are thought to include Barton Mills, Worthing Junction, Andover and Battledown.
The project covers the design, installation and commissioning of a control centre and 185 new signals covering more than 60 miles of line.
Atkins declined to comment.