In the dying days of the 2010 general election, too late, far too late, one event electrified the campaign. Citizens UK, the living wage community organisers, held a leaders’ hustings under the high dome of London’s Methodist Central Hall. In a heart-stopping moment, a 14-year-old girl, Tia Sanchez, stepped up to the lectern and told of the hardship of her family’s life.

She pointed out two women: “This is my mum, Sandra, and my grandmother, Marta.” Then the bombshell dropped. “They work as cleaners in the Treasury.” They had cleaned Gordon Brown’s office when he was chancellor, for an outsourced to a private firm that paid poverty wages. She said what a difference a living wage would make. “I might get a laptop I need for homework. We wouldn’t have weeks where we just eat lentils. My mum could afford to take the tube instead of three buses, and I would have three more hours of her time a day.”

She broke down in tears. Brown stepped up to give her a hug. That spurred him on to make the best speech of the campaign

She broke down in tears and Gordon Brown stepped up to give her a hug. That spurred him on to make the best speech of the campaign, pounding with indignation: “Wealth must serve more than the wealthy, prosperity must serve more than the prosperous and good fortune must help more than the fortunate.” Many said that if he had stormed the country proclaiming his great mission on child poverty, he would have exposed David Cameron and George Osborne as pitifully hollow vessels.

What became of Tia Sanchez? Several times over the years I tried to find her, but her family worried they might lose their jobs if they said more. One Whitehall cleaner who had the audacity to give a letter to Tory minister Francis Maude, complaining of poor pay and working conditions, was punished by the company for “gross misconduct” and moved to a job that he found more difficult. After that the Sanchez family vanished, losing touch with Citizens UK.

But Tia recently got back in touch, and we met in a cafe near where she lives in Tottenham, north London. Hers is a story of tragedy and fortitude against all the odds, a story of these times. First the good news: she worked hard at school, the only one of four siblings to reach university. She graduated a year ago from Royal Holloway with a first in human resource management, a triumph (and a heavy debt). Like so many graduates, she has applied for a thousand jobs of every kind, but employers require experience. She thinks a master’s degree might help, but that costs £10,000. She works in Tesco and shares a flat with three men she doesn’t know. Horrible, she says, but at £500 a month, it’s the cheapest she can find.

Thousands of young people face homeless Christmas, charity says Read more

She is all alone in the world, her brothers scattered. While she studied for her degree, she nursed her mother, who died of pancreatic cancer aged 49. Her grandmother has severe dementia and returned to Spain. Tia, now using her full name Thiara, started to cry as she remembered the hardship of her beloved mother’s life. When they were evicted from one flat, the family spent three months living rough, sleeping on buses and park benches, missing school, until they were rescued by Catholic nuns. They moved rented homes often. “Most of all, I minded hardly seeing my mother. She came home so late, so tired, she just ate and slept, getting up at 2.50am for work. We used to meet her halfway from work, so we could share her last bus home. We had no time together, no holidays.”

Now she wants to volunteer with Citizens UK, campaigning for employers to pay the real living wage – £9.30 outside London, against the government’s £8.21: Labour pledges an immediate rise to £10 everywhere. Its new “living hour” campaign demands a 16-hour minimum week, with four weeks’ notice of shifts. (Ikea, Aviva and Nationwide have signed up.) “That pay, those conditions, would have changed our lives,” she says.

Gordon Brown is making thundering poverty speeches this week. “I remember Tia well,” he tells me, eager to help her. “I remember that Monday before the election. Both Cameron and [Nick] Clegg made big poverty pledges they broke immediately. The Liberal Democrat anti-austerity manifesto was a worse U-turn than on student fees.”

Brown, who cut child poverty by a million, points to the treatment of poor people since he left office. He rails against universal credit, celebrating Labour’s plan to abolish it. He is appalled by the two-child limit and the cuts and long freezes to benefits, soaring numbers of families in private rentals, housing benefit no longer covering their rent. “They say they’re unfreezing child benefit? That’s just 35p, after they cut it by £7. I am utterly shocked by the levels of child poverty.” He quotes the Institute for Fiscal Studies’ 2017 prediction for it to reach 5.1 million children by 2022. He is appalled, above all, by the Tories’ indifference: “At least Thatcher and Major worried at rising numbers. Not now.”

A decent day’s pay for a decent day’s work – why are we still waiting for this? | John Sentamu Read more

Time was when poverty was prime electoral turf. Labour struggles to push it on to the agenda, but it makes no impact on the Tories and their press. There’s no lack of brutal facts: in the last week alone the TUC reported that wages are still £20 below 2009 levels, with household debt at its highest. The Resolution Foundation finds the “jobs miracle” is due to poor people being driven to take on extra work. Fidelity says half of non-home owners now doubt they will ever own. The Trussell Trust reports the steepest rise in food-bank use in five years, while the Royal Society of Arts, Manufactures and Commerce finds four in 10 don’t believe they’ll have a decent standard of living in 10 years’ time – “the new normal”.

Unsurprisingly the Office for National Statistics finds levels of debt and anxiety rising. Worse, forthcoming Child Poverty Action Group analysis finds the poor are poorer – those living below the poverty line (60% of median income) have fallen another 30% beneath the threshold. There is no sign that Boris Johnson feels any need to pretend to be concerned about the millions of Thiaras barely scraping a living.

• Polly Toynbee is a Guardian columnist