Network Rail demanded answers from the contractors, asking why assurances given to Network Rail before Christmas proved to be wrong.
Iain Coucher, Network Rail's chief executive said: "Far too many passengers were inconvenienced over the holiday period and we are taking that very seriously.
"We at Network Rail have taken responsibility and we reiterate our apology. Nonetheless, I wanted personally to hear explanations from the relevant contractors. What happened was totally unacceptable and we have to learn lessons, so it does not happen again."
The findings from these meetings will be fed into Network Rail's ongoing investigation into the New Year passenger disruption and will be presented at the Network Rail board meeting on Jan 16th, and then to Network Rail members on Jan 18th.
The Office of Rail Regulation is conducting its own investigation into the dealys.
The work at Rugby included:
o Installing over 5km of overhead line
o Bringing into use 5.3km of new track
o Bringing into use 15 new sets of points
o Installing two new sets of points
o Bringing into use 18 new signals
o Making 16 new track connections
o Demolishing a mini-signal box
o Removing 11 sections of overhead wire and moving a further 14
o Removing four signalling gantries
o Installing nine new signalling 'booster' cabinets
Work at Liverpool Street involved the demolition of a bridge, known as GE19, which is 120 years old and has been out of use for decades and is no longer safe to use. It is also in the wrong position for new East London Line tracks.
Demolition involved removing some 12,000 tonnes of brickwork. The new bridge will be the length of three Wimbledon Centre Courts and will be installed in Spring 2008.