Personal Independence payment ((PIP) is failing in its primary purpose of cutting the benefits bill, according to the Office for Budget Responsibility (OBR).
The government introduced PIP with the aim of cutting spending on disability benefits by 20%.
However, a predicted spend of £13.6bn on disability benefits in 2018-19 is now forecast to be £18bn.
Frank Field, chair of the Work and Pensions select committee told the Independent:
"Clearly the Government was as over-optimistic with PIP as it has been with universal credit.
"Its failure to deliver either project on time, as well as to achieve the savings it had assumed would be possible, has resulted in a series of cuts having to be made elsewhere in the welfare budget. One way of saving money, of course, would be to ensure a higher percentage of PIP assessments return accurate decisions.”