Network Rail plans to investigate why engineering work on the West Coast Mainline, has over-run. So, who employs these shoddy workers that Network Rail plans to investigate? Er, Network Rail.
In other words, they are have 'launched an investigation' into work which a competent organisation would have been managing and monitoring in the first place. Indeed, it is one of the central reasons why Network Rail exists. It is like Basil Fawlty blaming Manuel for his own management shortcomings.