The number of people in the UK living in relative poverty has risen for the first time in almost a decade.
Just over 10 million individuals were estimated to be in relative low income - below 60% of average household income - in 2014-15.
This is a rise of half a million on the previous year, according to new figures from the Department for Work and Pensions.
The number of children living in poverty has also risen for the first time in nearly 10 years.
But average household income is now back above levels last seen before the 2008/09 financial crash, hitting a record high of £473 a week in 2014-15.
The Resolution Foundation described the rise in average incomes as "encouraging" but said the increase in child poverty was "concerning" and warned that uncertainty surrounding the EU referendum presented "a clear downward threat" to incomes in the short term.
Stephen Crabb, the work and pensions secretary, hailed the rise in average household income as a "sign of a strong economy" that is "benefiting people across the UK."
A total of 10.1 million individuals were estimated as being in relative poverty in 2014/15, compared with 9.6 million in 2013/14.
This is the first year-on-year increase since 2007/08. It is also the highest figure since 2009/10, when the number was 10.4 million.
Child poverty rose by 200,000 in 2014/15: the first increase since 2006. The total number of children in relative low income is 2.5 million.
Mr Crabb acknowledged there is "still more to do" in tackling poverty.
"Our Life Chances Strategy will look at the root causes of poverty, whether that's worklessness, debt or addiction, family break down or educational attainment," he said. "It's only by doing this that we can truly tackle poverty and ensure everyone succeeds in life."
David Finch, Senior Economic Analyst at the Resolution Foundation, said: "It's a concern that the welcome income growth in recent years has failed to make any inroads into reducing high levels of child poverty in working households.
"And while income growth has been positive in recent years, the outlook of weaker pay growth, significant welfare cuts and now higher inflation stemming from the Brexit sterling plunge means the living standards of many families may come under strain in the coming years.
He added: "Given the challenging outlook for living standards, its right that the new government takes stock and thinks again on major reductions to working age benefits that are set to seriously undermine the incomes of low income working families in the coming years."
Alison Garnham, Chief Executive of Child Poverty Action Group, said: "Our children cannot afford for the Government to be distracted by Brexit and lose control of child poverty.
"A decade ago, when David Cameron became party leader, he promised that under his leadership his party would measure and act on child poverty. It's a tragedy that we are now talking about rises in child poverty not falls.
"It's also hugely depressing that at a time when we're seeing rising child poverty the Government has passed legislation that eliminates its target to reduce child poverty, or even to report on the progress it is making."