There is no such thing as criminal negligence in English law other than manslaughter by gross negligence. Other than that exception, negligence is a tort - a civil wrong - not a crime.
There are three offences of fraud, which are found in
sections 2 to 4 of the Fraud Act 2006. Of these, the most generally applicable is section 2 fraud by false representation. All three offences have a common
mens rea of dishonestly carrying out the fraudulent act intending to make a monetary and/or property gain for themselves or another, to cause another to lose money and/or property, or to cause another a risk of losing money and/or property. Following
Ivey v Genting Casinos [2017] UKSC 67, the test for dishonesty is "dishonest by the lay objective standards of ordinary reasonable and honest people" (the second limb of the former
Ghosh test is no longer law).
I think it would be a long stretch to turn 'staff members being sucked into the project wide group think that we can get this done, notwithstanding growing evidence that we cannot' into establishing beyond reasonable doubt that 'one or more individuals each made a statement that the project was on track when it wasn't, knowing these statement to be untrue, intentionally exposing the project funders to a risk of loss and that the statement was dishonest in the eyes of lay people'.
The biggest barrier to a fraud prosecution is likely the requirement for intention. An individual making a dishonest statement about progress that they knew could expose the funders to a risk of loss is not enough - legally speaking that is being reckless (knowing of a risk that you go on to take) about exposing funders to a risk of loss. The act must have been intended to expose the funders to a risk of loss for there to be any possibility of fraud.
Further, statements on whether a project is on track would likely be covered by hedges and would likely be made collectively by a group of managers or a board, not a particular individual. The chief executive reporting "It is the opinion of the board of Crossrail Ltd that the project is on target for opening on time, subject to the remaining work proceeding as expected" is a very different thing from one individual stating "Crossrail will open on time".
As anyone who has followed this debacle knows, there are unanswered questions about the scrutiny of Crossrail Ltd's statements by TfL and perhaps also the DfT, which is a further complication.
Any legal remedy the funding bodies might have likely lays in contract law, as this offers wider scope for obtaining damages than tort law. There is a specialist sub-division of the Queen's Bench Division of the High Court known as the Technology and Construction Court that exists to deal with precisely this sort of dispute.
As for individual staff members, what happens on any dismissal by their employer is subject to their contract of employment and employment law.