Not sure if this'll help, but I was an undergrad at RHUL doing a history BA, and I could take (and did) one history module at UCL this year. I think one reason this worked is because the School of History in the University of London allows students from some of the colleges to do courses elsewhere. However it is slightly restricted e.g. I couldn't do a course at SOAS, Birkbeck or LSE due to term date incompatibility/having to pay extra fees on top. However it may be different for different colleges e.g I've heard of people from UCL doing courses at LSE, so it depends on the arrangements colleges have with each other.
From my experience you can only take one course (i.e. one unit) outside your department or college a year.
I agree with the second poster about asking your department at QMUL and the Dept. of Scandinavian studies UCL where you stand, as there are certain criteria and they'll know how to direct you.