The report in the Journal of Commerce that the Norfolk & Southern Railroad in the US managed to upgrade a 100-mile section of track in an 8-day blockade, demonstrates just what can be done if there's a will and a way. The journal reports that "They laid 29 miles of new track, resurfaced 69 miles’ worth, replaced three bridge decks and improved track signaling". Apparently, they needed 400 people working on the project. I sometimes wonder if we have that many railway engineers available in Britain.
We don't know the exact circumstances of the project but, even if we could work at a quarter of that rate in Britain, we'd be doing better than we are now. Network Rail, please note.