The letter states: “By every measure, parents in these households will be unable to meet the basic needs of their children.
“They will be trapped at an income level that is inadequate by a wide margin to meet their children’s needs. This runs completely counter to the Government’s stated intentions of ensuring that those who are in work are rewarded fairly, and is particularly inhumane.”
A spokesman for the Department of Work & Pensions said: “Our welfare reforms are restoring fairness to the system for those who use it and those who pay for it.
"This reform ensures people on benefits have the same choices as those supporting themselves solely through work. But we have always been clear that exemptions will be in place, which is why we are consulting so they can be delivered in the most effective, compassionate way possible."