The number of children growing up in poverty in working households has shot up by 38% since 2010, according to the TUC.
It says the 800,000 overall increase to a total of 2.9m nationwide has hit London, East of England and West hardest.
The TUC says 485,000?children in working households have been pushed below the breadline as a direct result of the Government’s in-work benefit cuts.
Other key factors behind the rise in child poverty are weak wage growth, the spread of insecure work and population growth.
The TUC is calling for a range of reforms including raising the minimum wage to £10 an hour, scrapping the Universal Credit, banning zero hours contracts and giving workers new rights to join unions.
TUC general secretary Frances O’Grady said: 'The Conservatives’ cuts to in-work benefits have come at a terrible human cost.
'As too has their failure to tackle insecure work and get wages rising across the economy.
'We need a government that puts working families first, not wealthy donors and hedge funds.'