In this May 2021 paper, the Institute for Public Policy Research (IPPR) traces "the emergence of a poorly understood social challenge and one which symbolises Britain’s broken ‘social settlement’: the continued rise in working poverty since the beginning of this century." Available as a PDF and in other formats, here.
The Joseph Rowntree Foundation continues to be one of the most reliable sources of data and analysis on UK poverty. Their UK poverty 2019/20 report can be accesed via their site, here.
"Being in poverty means different things to different people. That’s one of the reasons we have so many possible ways of measuring it in the UK. So one of the most valuable questions to ask anyone who makes claims on this topic is: what do you mean by poverty?"
Full Fact is the UK's independent fact checking charity. See their work on UK poverty facts.