3.88 million to 583k is certainly a collapse. Much of that was down to them being seen as a single issue party but also because they were so identified with Nigel Farage. Nuttall was clearly a joke of a leader and the party has embarrassed itself badly in the last year.
The assumption before the election, a mistaken one, was that the UKIP vote would transfer to the Tories en bloc. A lot of it did but not in the absolute numbers expected. The combined Tory/UKIP vote declined by almost a million in 2017 from what it was in 2015.
An examination of where the UKIP vote actually came from in the first place is probably needed to explain where it went in 2017.
A lot would have been ex-Tory support which returned to the Tories in 2017, and many of those would have been attracted back to the Tories by their drift rightwards, but there was definitely also a smaller but sizeable element of former Labour support which was attracted by UKIPās rhetoric on the economy and public services. They returned to Labour in 2017.
There was also a sizeable protest element to their support , many of whom wouldnāt have voted at all previously.
The dynamics of the Brexit vote were similar. It wasnāt all a Little Englander, harking back to the Empire, anti-immigrant vote, clearly a lot, probably a majority of it was, but a lot of it was a protest vote, and/or low information voters who are sick of austerity and thought any alternative couldnāt be worse than the present situation.
I donāt think the way right-wing populist or far-right parties currently operate in Europe is sustainable. Most people find their rhetoric abhorrent, but they also have a basic problem in terms of competence or the perception of competence - they tend to be chaotic messes with unworkable policies. UKIP and Le Penās party both have serious problems in this regard. Trump has badly damaged them by association.
A key characteristic of most of these parties or movements is their identification with one charismatic individual - UKIP with Farage, the French National Front with Le Pen or the Le Pen family, Geert Wilders in Holland and obviously Trump in the US. When they move on, thereās not much left.
All of these parties and the individuals who lead them have fundamentally dystopian worldviews. Thereās only so long this type of negative politics can last. The Tories now find themselves associated with this type of politics and that will be a big problem for them going forward.