Single parents with children under two should be exempt from Iain Duncan Smith's controversial benefits cap that causes them "real misery", a High Court judge has ruled.

Mr Justice Collins said the lone mums and dads are being unjustly discriminated against by the government and the cap is "unlawful" when applied to them.

The Department for Work and Pensions hit back by saying the cap "incentives work" with single parents able to claim £29,000 in benefits in London.

The judge's decision came after four single mums launched a legal challenge against the caps, introduced by the Mr Duncan Smith while Work and Pensions Secretary under David Cameron.

Lawyers for the families said that a reduced benefit cap, introduced last year, "drastically reduced housing benefits, leaving lone parent families across the country unable to afford basic life necessities to care for their children".

Mr Justice Collins said the successful claim related to the "revised" benefit cap which "requires the parent in order to avoid the imposition of the cap to work at least 16 hours per week".

He announced that the regulations are "unlawful insofar as they apply to lone parents with a child or children under the age of two", as they involve "unjustified discrimination" against parents and children.

Labour leader Jeremy Corbyn said the ruling shows "further demonstration of the failure of this government's austerity agenda".

Representing the families, solicitor Rebekah Carrier said: "Single mothers like my clients have been forced into homelessness and reliance on food banks as a result of the benefit cap.

"Thousands of children have been forced into poverty, which has severe long-term effects on their health and well-being."

After giving his decision on Thursday he gave the Government permission to appeal.

A DWP spokesperson said: "We are disappointed with the decision and intend to appeal.

"Work is the best way to raise living standards, and many parents with young children are employed.

"The benefit cap incentivises work, even if it's part-time, as anyone eligible for working tax credits or the equivalent under Universal Credit, is exempt.

"Even with the cap, lone parents can still receive benefits up to the equivalent salary of £25,000, or £29,000 in London, and we have made Discretionary Housing Payments available to people who need extra help."