SOUTHEND-ON-SEA, England — First she stopped heating her apartment, putting furniture in front of the radiators to try to forget they were there. She unscrewed most of the light bulbs, turned off the hot water, and sold her iPhone, her watch, her television and even her curtains to feed herself and her 2-year-old son.

Then she wrote about it in a blog post titled “Hunger Hurts” that soon spread widely. “Poverty is the sinking feeling when your small boy finishes his one Weetabix and says, ‘More, Mummy, bread and jam please, Mummy,’ ” she wrote, “as you’re wondering whether to take the TV or the guitar to the pawnshop first, and how to tell him that there is no bread or jam.”

Jack Monroe, a 25-year-old single mother who changed her name from Melissa because “I’m just not a Melissa,” is an unlikely ambassador for the growing ranks of Britain’s poor — and now one with a $40,000 book contract. Her sudden slide into poverty two years ago and her plucky online diary, A Girl Called Jack, chronicling the reality of life on the bread line have turned her into a celebrity in Britain. She is now courted by politicians, charities and even supermarket chains, and people regularly ask for her autograph.

Ms. Monroe, who left school at 16, has more than 31,000 followers on Twitter and now writes a weekly food column for the newspaper The Guardian, featuring recipes costing less than one pound ($1.64) a person. Her austerity cookbook is due out in February. More than once has she been told that she does not really “seem poor.”