i don't actually know for certain as i don't know anyone who's been interviewed by them for psychology, but i would imagine it would be fairly formal, 'cause it is goldsmiths afterall
i have an offer from them for psychology too, actually, and they didn't want to interview me. i imagine you must have pretty good grades though, if you're applying for UCL? so i can't see why they would, hmm. but good luck! i'm sure you'll be fine.