His refusal was confirmed by a senior civil servant just as Osborne was preparing to deliver a budget seen by many campaigners as another attack on disabled people's living standards, in which he slashed future support for hundreds of thousands of people on out-of-work disability benefits.

Only recently, Disability News Service (DNS) revealed government figures which showed that disability poverty rose sharply in the fourth year of the coalition government.

Last summer, the Equality and Human Rights Commission (EHRC) published a report that concluded that assessing the overall impact of welfare reforms and spending cuts on disabled people was "feasible and practicable", despite ministers repeatedly claiming such a task was impossible.

The report also concluded that disabled people had been hit disproportionately hard by the government's welfare reforms.

The report was part of work the EHRC was doing with the Treasury and other government departments - including the Department for Work and Pensions - to examine ways of "making financial policy fairer and more efficiently targeted".

Disabled activists and other campaigners have been demanding since at least 2011 that the government carries out a "cumulative" assessment of the impact of its spending and benefit cuts and other welfare reforms on disabled people.

But work and pensions ministers under the coalition repeatedly ridiculed the idea, even though their own social security advisory committee said it could and should be done.

Now, in the first evidence session of a committee set up by the House of Lords to examine the impact of the Equality Act 2010 on disabled people, a senior civil servant has admitted that attempts to persuade Osborne to carry out such an assessment have failed.

The admission came less than 24 hours before the chancellor delivered his budget speech.

The disabled peer Baroness [Sal] Brinton (pictured), president of the Liberal Democrats, had asked the panel of senior civil servants if it was possible to see a Treasury assessment of the cumulative impact on disabled people of "a whole string" of cuts to their support, such as the closure of the Independent Living Fund, and the introduction of the bedroom tax and benefit caps.

But Charles Ramsden, head of the equality framework team for the Government Equalities Office, told her that the Treasury "does not accept the scope for doing cumulative impacts across government", and that "agreement on that important area and one or two other points has not been reached finally".

An EHRC spokesman told DNS today (Thursday): "During the last few years, the commission has influenced the work of HM Treasury and key central government departments to improve the way that equality considerations are taken into account in financial decision-making.

"Earlier this year, we published a report which recommended the steps the government should take to ensure budget and spending review decisions are as fair as possible."

These steps included assessing the combined effects on different groups, such as disabled people, of a range of spending decisions, he said.

He added: "We will maintain a watching brief on the work by the Treasury to continue these improvements, including in the context of the 2015 spending review later this year."

But he has so far refused to confirm that discussions with the Treasury have now concluded, and that the Treasury has refused to carry out a CIA, despite Ramsden's comments.

The Treasury said it was "fully compliant" with its public sector equality duties when taking policy decisions, which included "considering the impact of measures on people with disabilities and if any mitigating action is appropriate".

A Treasury spokeswoman said: "We have completed assessment of all individual measures in line with our statutory duties."

But she later admitted that the Treasury would not be carrying out any cumulative assessments.

She said: "We can't do a cumulative technical assessment because we don't have the modelling capability to do so.

"The survey which underpins our model doesn't contain enough information on disabled people to do a robust qualitative assessment."

Meanwhile, in a blog by the commission's chair, Baroness Onora O'Neill, published on Sunday (5 July), she warns that one of the "big themes" of Is Britain Fairer?, the EHRC's five-yearly report on progress towards equality and human rights, due later this year, was "likely to be about life in Britain in 2015 for many disabled people, and their opportunities to participate in our society".

She says in the blog: "The data shows concerns in a number of different areas, including participation in the labour market and some aspects of care and support for people with severe disabilities