BA then completely unrelated MSc?

Is it possible to do a BA in one subject and then go on to do a masters in a completely different subject? For example, I was thinking of doing a geography degree and then a conversion course in pyschology.
Would this be possible or does the BA need to be social, clinical or life science discipline that is relevant to pyschology?

Just speculating here, but I would assume that if you show interest and have relevant background skills it should be doable. Breaking down geography, physical geography might not help all that much content-wise but you'd be surprised by the overlap in human geography. Both I assume would provide the base educational and research skills so it should be doable. That's what the conversion courses are for anyways, to catch you up in content, aren't they?
I just always think about my friend who did her BA in Theology and is now doing an MSc in Environmental Sustainability.