Coucher said of the Rugby job, "We were overambitious, but for the right reasons. We wanted to get the work done and still be on time."
According to Bechtel's managing director of its rail division, Tom McCarthy, who act as Network Rail's programme managers, three 'readiness reviews', which simulated the work around Rugby hour-by-hour, had been conducted 8 weeks, four weeks, and 1 week before the work began.
He said that they had also sought additional assurances from the contractors for the job, Jarvis, that enough staff would be available, and had asked details of agencies supplying workers.
McCarthy said Jarvis had given the details of Oracle Global, which had satisfied them that enough staff would be available.
Under questioning, Mccarthy said, "At its lowest point we were getting less than 50% of those resources we needed from the contractor."
When the staff shortages became apparent, Bechtel tried to tap into Network Rail's qualified staff from around the country, but people were already engaged in other jobs.
McCarthy said that around 65 people would were needed, split into two 12-hour shifts. He said that they were still trying to establish why the staff failed to show-up.
When the overhead line work was finally up at Rugby, bugs in the system prevented the new line going live. "There were more snags than anticipated. It is the most complex piece of rewiring since rewiring Euston," said Coucher.
The cost for the disruption is not yet known, but Coucher said it would be, "In excess of £10M".
In a separate session, chairman of the Office of Rail Regulation Chris Bolt said he had turned down a request from Virgin Trains to disallow additional work days to complete the job.
Bolt said, "We looked at the impacts of saying they could not, and we decided that not agreeing to the extra days would have prejuduiced timetables," and the work at Rugby was essential to complete the outputs demanded by the government in the High-Level Output Specification in the summer.
The New Year disruption is thought to have impacted 250,000 people.