I don't think this is the real deal - the application for registration was submitted the day after the first announcement about GBR was made; there are only 100 shares in the company (each of £1.00) and all are held by one person, a Mr Michael Moir who is also the sole Director; there are no other persons registered as having significant control; and the top Google result for the service address of 160 City Road EC1V 2NX is a firm that will lease you the right to register a company at said address for £29.00 per year (with forward of mail included!).
By comparison,
Network Rail Limited is registered as a private company limited by guarantee
without share capital, at NR's actual head office address of 1 Eversholt Street NW1 2DN, and most instructively shows the Secretary Of State for Transport as a person with significant control over the company. You'll also find that the DfT as a body is shown as having significant control over many of the legacy BR companies.
As an amusing aside, there's also a
Great Britain Railways Limited that was incorporated only four days ago and is registered to a "website manager" at a private flat in SW1P 4EY.