The monopoly of Spain's traditional political heavyweights is set to take a hit as two new contenders fight for power in national elections on 20 December.

Left-wing Podemos and Ciudadanos (Citizens), who sell themselves as a party of the centre, are riding high in the opinion polls and could change the face of Spanish politics.

Citizens leader Albert Rivera launched his party in 2006 posing naked on campaign posters while Podemos (We Can) only emerged last year, led by charismatic university professor Pablo Iglesias.

Tom Burridge looks at their rise.