It is not known if exactly 48 percent has come from, but some credible sources have put the figure at around 50 percent.
According to a 2018 House of Commons report called Child Poverty in London, "a person is in absolute low income if their household income is below 60% of median income in a fixed year (2010/11), adjusted for inflation." The report also states that poverty rates are much higher in London than in other areas of the U.K. "Around 700,000 children in London were in relative low income in 2013/14 to 2015/16 after accounting for housing costs," the report reads. "This was 37% of all children in London, the highest rate of all countries and regions of the UK. The equivalent UK rate was 29%."
According to Trust For London, a charity that tackles poverty and inequality whose most recent data is from 2013/14, Harringey—the Borough of London in which Tottenham is situated—has a child poverty rate of 34 percent. Their data also shows that the area with the highest poverty rate is in Tower Hamlets, which is a borough in East London.
A charity called End Child Poverty says that the district of Tottenham has a child poverty rate of 50.2 percent for the year 2018/19, making it one of the most deprived areas of the capital. As well as this, David Lammy, the Labour MP for Tottenham, has also tweeted that Tottenham has a child poverty rate of above 40 percent, adding that Institute for Fiscal Studies (IFS) has predicted that child poverty in the area would increase by 50 percent in 2020.
In short, it is difficult to see where the exact figure of 48 percent has come from. However, credible sources have stated that child poverty rates in the Tottenham area lies in the region of 50 percent. With this in mind, we find this claim to be partly true.