Critical thinking is very important to this essay, also it requires a wide reading, journals will be particularly beneficial for the references.
The University uses a variation of the Harvard referencing style called Leeds Harvard. Family name, INITIAL(S). Year. Title. Edition (if not first edition). Place of publication: Publisher.
eg: Bowlby, J. 1998. Separation. Attachment and loss series, Vol 3. 2nd ed. London: Routledge.