Thank you for posting that YouTube link, GracesGran. I hadn't seen it before. Matthew Goodwin was the co-author of the book I mentioned before. His talk (2014, so the same time as the book) summarises the book quite neatly. The book contains further details, such as research methodology, sources and full data tables.
Goodwin is an academic political scientist, not a politician. This is an interpretation of the data and does not include value judgements. He uses the term 'left behind' as a shorthand for certain demographic groups. Before 2014 it was thought that UKIP supporters were mainly Europhobic Tories, but his work showed otherwise. This was quite ground breaking in 2014, because politicians hadn't accepted how much support was coming from former Labour voters.
Analysis of the 2015 election results and, even more strikingly, the referendum result shows how right Goodwin was. UKIP seems to be having its own problems now, but some people, such as Arron Banks, understand the implications of Goodwin's work. Hence the talk about parking UKIP's tanks in Labour strongholds and Nuttall's attempts to appeal to what Goodwin describes as the 'left behind' groups. What we're seeing is an attempt to inflame populist feeling. Whether or not UKIP has the organisation and discipline to become a serious political party remains to be seen. The other political parties ignored 'popular' discontent and are paying the price - well, Labour is - the FPTP voting system will probably keep the Conservatives in power, despite their unpopularity.
PS. I'd like to comment on many other posts, but I'm a bit short of time and don't want to flood the thread with my thoughts anyway.
PPS. I recommend watching the video, although populism is, of course, not confined to the UK nor is it entirely right-wing.