The grandfather of a severely disabled teenager has challenged David Cameron to explain why the government is appealing against a judge’s ruling that the bedroom tax violated his family’s human rights.

Paul Rutherford, from Pembrokeshire, said he was “mad angry” at the government’s response after the lord chief justice, Lord Thomas, and two other court of appeal judges declared that the bedroom tax had not been justified in the family’s case.

Rutherford said he was initially “happy, over the moon, delighted” by the ruling, after a two-year legal fight, but dismayed after the Department of Work and Pensions (DWP) confirmed it would appeal the ruling at the supreme court.

“It was a relief from all the stress,” he said, speaking from his home in Wales. “But I’m mad angry because they’re appealing. I would like David Cameron or Iain Duncan Smith to explain why they are spending taxpayers money on an appeal? Why are they doing this to me and other families?”