seeyou is using wikipedia's definition, but I've looked through the site, and nowhere do they actually define what they are using as indicators.
In the report itself, they talk about making adjustments to various pieces of data, but their baseline is using the numbers of families who receive out-of-work benefits or in receipt of WTC with an income of lower than 60% of the median. (This is a close paraphrase). They say that this over-represents the number of unworking poor, and under-represents the working poor, so figures are adjusted up or down to compensate for this. There is no information on how this has been done.
In short- if this was an academic paper, it wouldn't be published. If a student produced and submitted a report like this, it would receive a failing grade as is. CPAG are an action group with a specific agenda, which names Osborne who "wants to take even more from the poorest families in your area by cutting tax credits which help working families."
Child poverty is a problem in this country - but this report allows no-one to have confidence in its figures (who was it who said there are lies, damned lies, and statistics?!) and the use of the Osborne example is emotive but imo undermines what ought to be a very important issue through cheap political point scoring.