Sir Keir Starmer has hit out at Britains top economic watchdog after it refused to accept Labours claim that controversial benefit cuts will get a significant number of people back into work.
The Prime Minister said he personally struggled with the Office for Budget Responsibilitys (OBR) approach in assessing a package of welfare reforms in the Spring Statement.
While in opposition, Sir Keir lauded the OBRs work in holding the last Conservative government to account.
The Budget Responsibility Act, which strengthens the OBRs role, was the first piece of legislation introduced by Labour after the election.
But in recent months, ministers have become increasingly frustrated by the OBRs refusal to simply take their word for the impact their policies will have.
Chancellor Rachel Reeves was forced to bring forward benefit cuts last month after the OBR ruled that her package would not raise the £5billion claimed by the Treasury.
An impact assessment by the Department for Work and Pensions found the cuts to disability benefits would push 250,000 people into poverty, including 50,000 children.
To the fury of ministers, neither assessment took account of £1billion worth of back to work measures.
Sir Keir Starmer, pictured in Parliament on Tuesday, previously lauded the OBRs work in holding the last Conservative government to account
Rachel Reeves was forced to bring forward benefit cuts last month (Pictured in Birmingham on Monday)
But the OBR said last month that it was unable to incorporate most of the supply-side impacts of the plans due to insufficient information from the Government on the policy details and analysis of their likely economic effects.
Yesterday Sir Keir insisted that the OBR should have given ministers credit for the package anyway.
He told Parliaments cross-party liaison committee: On the impact assessments, it is significant to my mind that the ability of any policy or legislation to change any behaviour at all is not priced in.
In other words, the OBR has scored nothing against any change here. The assumption is that not a single person changes their behaviour.
I personally struggle with that way of looking at it because I do think that these measures will make a material difference and they need to make a material difference.
But Kemi Badenoch mocked the PM for turning on the watchdog he had previously championed.
The Tory leader said on X: Labour literally passed a law in October requiring the Government to listen to the OBR. Now theyre criticising it.
It is another [Rachel] Reeves gimmick that shows they dont know what they are doing. From the Jobs Tax to snatching winter fuel payments, Labour are making everything worse.