I don't know if I can 'explain' it but there are definitely a good number of factors at play in Spain which aren't in Britain. As terrible as things are here, they are much worse in Spain and worse for more people, at over 50% youth unemployment for years it's difficult even for the most ardent traditionalist not to place blame on the economic system. Spain also has a much bigger 20th Century history of leftist opposition to the status quo, almost all of the active opposition to the Franco regime was Marxist or some variation thereof. The Podemos Party has grown out of the indignado movement which was significantly more successful than both the US Occupy, though I'm beginning to think that we may have underestimated the legacy of the US Occupy, and certainly our own token effort at doing the same.
No small measure of Podemos' success can also be attributed to an astute use of media to promote their message. Podemos' media effort has been led by Juan Carlos Monedero who participated in the very effective use of media by the Chavez government in Venezuela. The stuff they put out on their programme La Tuerka is just good, it's genuinely entertaining and talks about politics using common sense and accessible language.
Also, and I may be being just completely off base and ageist here or whatever, but I think that maybe part of what allows Podemos to galvanise the support of youth where groups like Left Unity are not able to is the composition of the leadership. Monedero and Pablo Iglesias are both relatively young and are to an extent unblemished by association with the failures of the traditional Spanish left and trade unions, they are outflanking them to their left in both action and ways of imagining a future politics in Spain whereas you look at Left Unity and it just seems like the same people making the same mistakes again with the same ideas that they were promoting or continue to promote in their own respective sects.
