A decision on airport expansion is being taken on the basis of "opaque" public figures, a senior MP warned.
Andrew Tyrie, chairman of the influential Commons Treasury select committee, said Parliament and the public had been left partly in the dark on the case for a new runway at Heathrow.
He has written to Chancellor George Osborne calling for more details of the calculations which led an independent commission to recommend the highly-controversial addition to the country's biggest airport.
The Davies Commission concluded it was the best of three shortlisted options which also include extending an existing Heathrow runway and building a new one at Gatwick.
In December the Government postponed a final decision pending new analysis of the environmental impacts.
In his letter, Mr Tyrie complained that ministers had failed to respond to a series of detailed technical questions tabled in the Commons seeking clarification in areas such as the impact on fares and passenger demand.
He said the Commission's case was "opaque in a number of important respects" and that "a good deal more information is required" if the Government's decision is to be properly scrutinised.
A Department for Transport spokesperson said the Commission had provided "exhaustive detail".
"The case for aviation expansion is clear and it's vitally important we get the decision right so that it will benefit generations to come," a spokesman said.
"So we continue to consider the exhaustive detail contained in the Airports Commission's final report.
"It has not so far been possible to respond to Mr Tyrie's long list of questions on related and different issues. However, we are considering his questions in the light of progress and will respond to his letter as soon as possible."
A spokesman for Gatwick Airport said: "This is a highly significant intervention from the Chairman of the Treasury Select Committee. It is clearly now the consensus view that the Davies Report is seriously flawed and not a sound basis for decision making."