What exactly is this UPyD anyway.
It's a sort of centrist Euroliberal party, stated ideology somewhat like the UK Lib Dems or Canadian Liberals. It's very personalist around its leader, though, like MoDem in France, but more successful mostly due to the electoral system. A big part of its platform is unflinching unitarianism (more robust than mere federalism), though. They're very opposed to any kind of regionalism or devolution, let alone independence movements (particularly the Basque separatists, but also the Catalonian nationalists, Galician nationalists, etc.).
They're both very left-wing? IU descends from the more "liberal" strain of western European communism and is consequently very much allied with the green movement. And ICV is of course on the left side of the green spectrum (more like the German Greens than the Canadian ones).