Amec and Carillion have ruled themselves out of the bidding for Thales Telecommunications Services, the firm that provides customer information screens for Railtrack.
TTS, owned by French defence group Thales, also has maintenance and infrastructure arms. It could be worth up to £200m.

Several firms, including Amey and Serco, have been approached as possible buyers, and a deal is expected in August.

An Amec spokesperson said: “I very much doubt that we would be interested. It’s unlikely that we would look at it given the likelihood of the Spie deal going ahead later this year. Acquisitions take up a lot of management resources.”

Amec owns 46% of French construction firm Spie and holds an option to buy the remaining 54%, now owned by half Spie’s 25,000 employees.

A Carillion spokesperson said the group was also unlikely to make a bid for TSS, which has more than 1000 staff and a turnover in excess of £100m.