All students can take an Erasmus year abroad; you don't have to be on a degree which specifically includes a year abroad. Some universities have an Erasmus page on their website where they tell you where you can study abroad, but many don't so you will have to contact each uni individually and ask for a list of partner universities where a Journalism student could study abroad.
Here are all the universities in London which do Journalism:
Birkbeck, University of London
Goldsmiths, University of London
City University London
University of Westminster
Kingston University
Brunel University London
University of East London
London Metropolitan University
Middlesex University
University of Roehampton
London South Bank University
University of West London