Media playback is unsupported on your device Media caption 'Nothing is off-limits' says Nicola Shaw

The executive asked to come up with a plan to revive Network Rail's fortunes has said she cannot rule out recommending privatisation.

In an interview with the BBC, Nicola Shaw said that a partial or total sell-off "was absolutely on the table; it can't not be."

Ms Shaw was drafted in by the government after Network Rail's upgrade plans fell apart last summer.

Work to electrify key lines had been dogged by delays and mounting costs.

Ministers paused two of the projects, in the Midlands and across the Pennines, and replaced the chairman, while a number of reviews are carried out.

Ms Shaw, who is the boss of Britain's only high speed line, HS1, was asked to come up with a report before the Budget next spring.

She said there were a whole range of issues that had to be considered and she was keen to hear what people had to say.

She said she would also recommend changes to the regulator if necessary.

A period of evolution

"I don't believe there is one perfect answer. I think there is something that we'll go forward with for the next period of evolution of the railway. I don't think there has to be a big row. The challenge for me is how to bring people together. To find a way forward that people will support."

The future of Network Rail - which controls 2,500 stations as well as tracks, tunnels and level crossings - has been up in the air ever since the embarrassing admission last June that, just one year into a five year upgrade plan, the company had lost control of timetables and budgets.

Problems came to a head when the company was re-classified as a public sector body in September last year.

Overnight, it meant it could no longer borrow extra money from private sources to fill the funding gap.

I've been told by those close to the situation that the impact of those changes took everyone by surprise.

It also meant the company's £37.7bn debt moved onto the government's books.

Difficult job

One source suggested that before the change "ministers might turn a blind eye" to the extra costs, as long as the job was done. This is no longer possible.

Insiders also talked of a failure to check if they had sufficient numbers of qualified engineers to carry out the necessary work.

And they underestimated how difficult it would be to upgrade and electrify the Great Western Line, which dates from Victorian times, while running a service on it.

Three reviews are under way.

One looking into what went wrong, due in a few weeks.

Network Rail's new chairman Sir Peter Hendy is looking at what they can afford to upgrade and how long it will take. It is likely to be published in November.

Nicola Shaw's report into how to change the structure and financing of Network Rail due in the spring.

Ms Shaw has a difficult job, navigating a wide range of views, including those of the unions and the new Labour leader, Jeremy Corbyn who wants to see the railways back in public hands.

"I am talking to unions, and to representatives of staff and to other members of different parties so I hope we have strong engagement because I think it matters."