Universal Credit isn’t working. Even the length of its delay (six years and counting) wouldn’t give me time to list all its problems here. The main ones are that it’s leading to debt, rent arrears (and therefore the risk of evictions), lower incomes for millions who rely on welfare, and a rise in food bank use.

But the Department for Work and Pensions refuses to engage with the hardship it is creating, according to MPs on the Public Accounts select committee. They accuse the Department of having a “fortress mentality”, whereby it is “failing claimants” with a “systemic culture of denial and defensiveness in the face of any adverse evidence presented by others”.

The committee’s report accuses the DWP of “persistently dismiss[ing] evidence that Universal Credit is causing hardship for claimants and additional burdens for local organisations and refuses to measure what it does not want to see”.

Anyone on the receiving (or non-receiving, if your case has been delayed) end of Universal Credit, or working with claimants, will have experienced the DWP’s characteristic blindness to glaring problems with the new welfare system.

Departmental spending cuts, the politics of welfare and an age-old tyranny of quotas means the DWP has a tendency to plough through with flawed initiatives without listening to its critics – even when ministers are told it could cost more money to administer than it saves.

The Department holds an odd role within Whitehall. It’s framed by wounded ministers as a whipping boy of the Treasury, a sorry symbol of central government austerity, yet is vital to the Prime Minister’s reputation: the benefit cap was a key – very popular – plank of Tory policy.

This gives it the toxic mix of bloody-minded commitment to policy with an utter refusal to take responsibility for its impacts.

In the case of Universal Credit, its “fortress mentality” should perhaps come as no surprise. From the very beginning when former Work and Pensions Secretary Iain Duncan Smith announced it in 2010, Universal Credit was intended to save money: to fix a “wildly expensive benefits system… No more spend and waste.”

In the same speech, Duncan Smith put benefit cuts in the context of needing to reduce the deficit – justifying then Chancellor George Osborne’s controversial child benefit cut as a decision which was “tough, fair and right” in that economic climate.

So yes, Universal Credit is dressed up in the language of “simplifying the system” and “making work pay” (in reality, it’s a bureaucratic nightmare that disincentivises single parents and second earners to work) – but it’s also a system designed by an aggressively state-sceptic government to save money. Universal Credit isn’t working for those who need it, but by making people worse off, it is fulfilling that key ideological task.

The architects of Universal Credit know full well that you can’t save money on welfare without people who rely on it suffering. So yes, the DWP is doubling down on a bad system. Why? Because it’s not the fortress that is paying for the problem; it’s the claimants who are under siege.