Alice Roberts argues in her book imaginatively titled "The Celts" that the Celts probably originated in Iberia and spread out from there, rather than the Alpine origin that I understand is commonly accepted. She also claims that this idea holds more currency amongst Spanish and Portuguese scholars than the rest of the West. Is this accurate? What kind of discourse has taken place surrounding the issue?
A first step there is to distinguish material culture from language : both are more considered apart in academia nowadays (presence of Halstattian or LaTenian influence in Jastorlf or Lusatian culture doesn't equal presence of Celtic speakers; and absence of these features doesn't imply a linguistic or immaterial radical difference as it was probably not the case between Late Iron Age Gaul and Britain). As there was no idea of a "pan-Celtic" identity based on language in Antiquity, and as the linguistic, archeological and political identities and phenomenons are more or less divorced; the origin of Celtic languages, Celtic material cultures (such as the question of Halstattian or Latenian expension) and Celtic proto-historical/historical peoples are to be considered separately.
The western hypothesis, supported among others by Barry Cunliffe, is less that Celts came from the Iberian Peninsula instead of coming from northern Alpine regions (a model identifying Celts with a radial development of the Iron Age cultures of Halstatt and La Tene, essentially abandoned since the 1990's) than that Celtic languages expanded from the Atlantic Bronze Age culture (trough encounter of Bell Baker and Corded Ware cultures), as a lingua franca being gradually adopted along the trade networks (John T.Koch proposes to consider Tartessian culture and language as Celtic) up to forming a linguistic continuum over Western, then Central Europe, during the Bronze and Iron Ages; while there were tentative proposition to identify the Urnfield Culture as a whole as the rough emergence of proto-Celtic speakers' cultures, the difficulties explaining the Celtic languages and peoples in western peripheries (British Isles and Iberian Peninsula) remain as important as with a strict identification with Halstattian/LaTenian cultures : several authors, such as Venceslas Kurta, already saw Bell Baker cultures as a possible first espace of emergence.
The Atlantic Bronze Age theory ( you'd find a sum in Celtic from the West) is seen with favour, at least a keen interest, even from some skeptics, but shouldn't be considered as definitely accepted for the moment : the Celticity of Tartessian language is still debated, concurrent model do exist (such as a polycentric emergence of proto-Celtic and para-Celtic languages), etc.
- Celtic from the West: Alternative Perspectives from Archaeology, Genetics, Language and Literature***;*** edited by Barry Cunliffe, John. T. Koch; 2012
- La préhistoire des Celtes; dir. Danièle Vitali; 2006