Ministers failed to take account of the impact on women, ethnic minorities and the disabled in key elements of its cuts programme, the official equality watchdog has found.
The Equality and Human Rights Commission said it was unable to determine whether decisions taken in the 2010 spending review were in full accord with the government's legal duty to consider their effects on equality.
In its first detailed review of a government spending round, the commission blamed a "lack of clarity" within Whitehall over where responsibility lay for particular decisions.
However it said it would be "disproportionate" to take any further formal action and praised the openness of ministers in co-operating with its review.
In its report, the commission cited three areas of concern. It said there was no evidence that any "gender analysis or equality screening" of the cap on household benefits was passed to Treasury ministers.
The potential impact of cuts to the bus service operators grant on the disabled was not included in the advice given to the Treasury, it said.
And there was no reference to ethnicity, disability or gender the information relating to decision to scrap the educational maintenance allowance and replace it with local discretionary funds.
The commission found that in six other cases - including ending the child benefit for higher rate taxpayers and reform of legal aid - decisions were taken by the Treasury in full accordance with its legal duties.
"The key point for the commission's work is not to judge the past, but to transform the future," said the commission's chair, Trevor Phillips.
"I am particularly pleased that the government has indicated that it will work with us over the next few years to make sure that the equality impact of policy is fully understood and taken into account before decisions are made.
"That we think will lead to more targeted spending, more effective use of public money, and above all greater fairness all round."
Shadow home secretary and equalities minister Yvette Cooper said it was further evidence of the Government's "deeply unfair" approach to cutting the deficit.
"Decisions by David Cameron and George Osborne are already hitting women and families hardest, helping millionaires whilst those on low and middle income pay much more," she said.
"Now this report shows ministers didn't even properly consider the impact of their plans on inequality in advance.
"This is a deeply unfair government. Time and again the vulnerable are hardest hit, and those on low and middle income lose out more than the highest earners."
A Treasury spokeswoman said: "In the spending review the Government had to take tough decisions to cut the deficit and put the public finances back on a stable footing. But the Government has made these decisions in the fairest way possible.
"The government takes equalities very seriously and at the spending review exceeded its legal duties."