A British government minister is being asked to put his money where his mouth is.

Opponents of a raft of welfare changes that took effect this week want Work and Pensions Secretary Iain Duncan Smith to make good on a claim that he could live on $80 a week — the amount one welfare recipient said he has left after paying for housing and heat.

Asked on national radio Monday whether he could get by on so little, Duncan Smith replied: “If I had to, I would.”

By late Tuesday, some 300,000 people had signed a petition urging him to prove it.

That would mean living on $11.43 a day in London, one of the most expensive cities in the world. It would also reflect a huge comedown — a 97 percent cut in his government minister’s salary.

Duncan Smith defended himself, telling a local newspaper that he’d been unemployed twice and knew what it was like “to live on the breadline.”

“This is a complete stunt which distracts attention from the welfare reforms, which are much more important and which I have been working hard to get done,” he was quoted as saying by the Wanstead & Woodford Guardian.

The Conservative-led government’s welfare reforms include changes in disability payments, below-inflation increases to benefits and, eventually, the replacement of a patchwork of housing, unemployment and parental benefits with one payment called the Universal Credit.

Prime Minister David Cameron has argued that the changes are needed to save money and make welfare more fair, but the tens of thousands of signatures garnered within 24 hours of Duncan Smith’s comments underscored the anger over the cuts and worry about their human impact.

“You would have to be really tight,” 28-year-old Amy Rowland said outside a London grocery store about the $80 a week budget. “You would have to constantly be thinking all the time, constantly watching your step.”

“What this government is trying to do is to put things right,” Treasury chief George Osborne told grocery store workers at a speech Tuesday. “We’re trying to make the system fair on people like you, who get up, go to work, and expect your taxes to be spent wisely. And we’re trying to restore hope in those communities who have been let down by generations of politicians by getting them back into work.”

The most discussed welfare change is a reduction in subsidies for social housing tenants who have spare bedrooms. Opponents have dubbed the measure a “bedroom tax,” but the government says the change will save money and free up housing for families because people with too many rooms will downsize.

Religious leaders, including the new archbishop of Canterbury, Justin Welby, have called the cuts “unjust,” and advocates for the disabled and anti-poverty campaigners held protest marches over the weekend. Activists argue that many people can’t just move — the country already has a dire shortage of public housing.

But it was the notion of Duncan Smith counting his coins at a supermarket that captured the public imagination as it illustrated how the poor really struggle to get by.

The weekly figure came from David Bennett, a market trader who said he earned about 2,700 pounds last year. He was interviewed by the BBC before Duncan Smith, describing how his housing benefit was being cut even though his children stayed with him several days a week.

If Bennett were to buy a monthly bus pass to get to work it would cost him the equivalent of about 2.50 pounds a day. Setting aside one pound a day for clothing and emergencies would leave him about 27 pounds a week, for food.