NETWORK RAIL has “many questions to answer” after admitting an engineering design blunder could spell further part closures on the Gospel Oak to Barking Overground line.

The route is reopening on Monday, February 27, after being down since June as part of works to electrify the route – which runs through Wanstead, Leytonstone and Walthamstow – and replace its two-car diesel trains with four-car electric ones.

Network Rail’s Anglia Route managing director Richard Schofield said the closures could last until early 2018 as structures carrying overhead wires were “incorrectly designed” and could not be installed.

The wires are necessary to upgrade the 14-mile line, with the late delivery of materials and structures creating even more delays.

Mr Schofield said closures will be required over a series of weekends, while a “full review into what went wrong” is already underway.

He added: “I sincerely apologise to passengers that we have not been able to complete all of the work in the time we set out, and for the future disruption we will cause to their journeys.

East London and West Essex Guardian Series:

This line is reopening soon, but for how long?

“I have instructed the project team to quickly deliver a robust plan to finish the work before new trains arrive next year, and passengers can be reassured that the line will reopen later this month to diesel trains as planned.”

TfL’s director of London rail Jonathan Fox said Network Rail did not inform TfL of the “significant problems” until “very recently”.

He said: “Londoners can be assured that we are pressing Network Rail for an urgent plan that explains exactly how this vital project will be delivered on time and with the absolute minimum further disruption to our customers.”

A furious London Assembly Member Caroline Pigeon said the fault for these delays rests with some appalling errors made by Network Rail.

She added: “I think TfL also need to explain why they were not aware of the significant problems until so recently.

“Their excuse that they were kept in the dark by Network Rail has a schoolboy sound to it, as anyone living close to the line could see that the electrification work had fallen behind schedule.

“It is bad enough that passengers in east London now face further closures over a series of weekends and almost certainly another full closure for a period of time later in the year.

“However it adds insult to injury to have Network Rail and TfL squabbling in public when their only priority should be minimising disruption for passengers.”

The upgrade is expected to double capacity and improve air quality along the line.

So far, five sections of the line have been lowered between Walthamstow Queens Road and Gospel Oak stations in preparation for the overhead wires.

Three electrical switching stations have been built and ten bridges have also been reconstructed and strengthened along the route while.