A Commons committee has attacked the Treasury for refusing to reveal analysis of how its decisions have hit women, minorities and people with disabilities.
Analysis of how changes might harm different groups was not released as part of an equalities impact assessment during the 2015 spending review.
MPs asked for a Treasury minister to explain the research carried out in the run-up to the statement but were knocked back by then chancellor George Osborne.
Requests for copies of detailed departmental assessments from the time, along with the Treasury's own review, were then rejected once Philip Hammond took over the role in the summer, according to the Women and Equalities Committee.
It was told "candid" discussions between departments and the Treasury would be compromised if the evidence was released.
The committee said the lack of information "demonstrates a concerning lack of transparency" and it was "disappointed" with the response from the Treasury.
Chairwoman Maria Miller said: "This Government understands the importance of equalities impact analysis and was the first ever to publish such an analysis for its 2010 spending review.
"The new equalities select committee has a mandate from Parliament to scrutinise Government's effectiveness in its equalities policies and this includes it effectiveness in using equalities analysis to evaluate policy changes.
"This report calls for more transparency in the process so that our select committee can look at how departments ensure the impact of policy change on equalities is understood. Without the information we have asked for or ministerial evidence it's not been possible to form a view of the Government's work under the public sector equality duty.
"Promotion of transparency is a central aim of the public sector equality duty requirements. The Government's current position means the evidence on compliance is incomplete."