The company, which owns and operates UK rail infrastructure including tracks, signals and stations, has confirmed it is conducting a closed list tender process to handle litigation, property and commercial matters.

Fifteen firms have been invited to submit a tender, including all of its existing legal panel members, with the process expected to finish early next year.

Although Network Rail would not comment about the firms on its existing panel, City giants Linklaters and Simmons & Simmons have both acted for Network Rail in the past. Linklaters advised the company on its acquisition of Railtrack and a £20bn long-term finance platform.

Company secretary Hazel Walker said: "Over the past three years we have restructured Network Rail’s legal services function and now is a good time to reassess our external support needs."

She added that, as the company is attempting to meet cost efficiency targets set by the UK rail regulator, it is asking tendering firms to submit ideas on how to improve cost efficiency.

Network Rail, which recently hit the headlines over its controversial succession to Railtrack, earlier this month announced a £4bn modernisation plan for several London stations, notably Euston, Victoria and Waterloo.