Transport secretary Grant Shapps is understood to have called in the chair of the review Doug Oakervee and prime minister Boris Johnson’s transport adviser Andrew Gilligan to request they push back the publication date.

The review had previously been expected to have been published by the Autumn, with an initial report mooted to have been given an approximate date of October 16 to be submitted to the Department for Transport.

The advisory panel to the independent review into HS2 has also been asked to sign new non disclosure agreements (NDAs) in an attempt to stop ongoing leaks, New Civil Engineer can reveal.

The new confidentiality commitments come after Shapps told Parliament’s transport select committee that media speculation about the review and its outcomes was “completely untrue”.

New Civil Engineer understands that within the Department for Transport (DfT), there are concerns that the review may be unable to address the issues raised within its terms of reference with sufficient thoroughness and could be open to potential challenge.

Speaking in Parliament, Shapps said: “In terms of timing. We always said autumn which runs up the end of the year. But as budget watchers will recall over the years, autumn can stretch into December. With Brexit we may have to let that process play out and then let members [of Parliament] concentrate on an issue like this [HS2] after.”

Railway engineer Michael Byng has told the Oakervee review that his revised cost of the project based on the recent Stocktake exercise undertaken by HS2 chair Allan Cook at £103bn in 2015 prices.

Additions to the cost, estimated in the Stocktake at £88bn, are a further £8bn to correct under-estimated property values and well as a potential £3bn for additional electrictity infrastructure to power the new railway. Byng also costed £2bn for depots for the line.

The Department for Transport has been contacted for comment.

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