To my understanding, Network Rail have only failed once, but as Klambert states, Railtrack and Jarvis were far worse.
And I also have to agree with Jamie (H222), there are so many switches to look after, especially on the West Coast Mainline, there are a lot of crossovers and express switches to maintain.
I think Network Rail has done some excellent work, in the refurbishment of railway stations across the country, and the re-work of the West Coast Mainline.
Also they have contracts for electrification of the GWR stretch from London Paddington to Reading/Didcot/Oxford/Bristol and other off lines, along with track improvement work and electrification of the Liverpool to Wigan/Manchester line via Huyton and Newton Le Willows.
I think Network rail have been the best so far.
Joe Airtime