Yesterday's settlement ended two years of horse-trading between Network Rail, the regulator and interested parties.
In the settlement, Network Rail accept that efficiencies must be driven-up so that government outputs set out in 2007's High Level Output Specification (HLOS) can be met.
However, according to the Association for Consultancy and Engineering (ACE), the efficiency savings have concerned its members - civil engineering consultants.
ACE chief executive Nelson Ogunshakin said: "The ORR's stipulation that Network Rail should cut costs by almost a quarter - on top of the 27% savings they have already achieved since 2004 - is deeply worrying.
"It will be enormously challenging to deliver the investment and operational improvement required in the railway while reducing costs. However, consultancy and engineering firms are keen to sit down with Network Rail to discuss how best resources can be optimised across the network to meet the stiff targets that have been set."
Ogunshakin said that ACE would welcome an early opportunity to sit down with Network Rail to discuss their plans.
"The next five years will see unprecedented investment in expanding the network and improving services. We want to work closely with Network Rail in partnership to deliver an effective and efficient rail network and a quality service to customers," he said.