A source close to the Department for Transport said that Darling was expected to announce who will carry out the review next week. It is expected to be more wide-ranging than previously thought.
The source said: "Darling is expected to announce the details of the plans through a parliamentary question next week."
He said that it was likely that the review would be carried out by someone with a strong financial background.
The Association of Consulting Engineers said it was looking forward to contributing.
A spokesperson said that the ACE shared Darling's concerns about the structure of the railways, as it hampered decision-making and led to disputes between vested parties.
He said: "However, streamlining and simplification must lead to real change and lasting improvements for passengers and those that work on the railway."
It is expected that the Strategic Rail Authority, created by Labour to get a grip on the industry, is to undergo the most detailed examination.