Use whichever referencing style you wish, although the Harvard method is probably the most widely used within UK academic institutions, due to its simplicity and ease of understanding.
If you have used the Harvard system the references are much shorter and contain each source listed only once in alphabetical order by originator’s name. This means that there is much less need for a bibliography but it could be used to list any sources not cited in the actual dissertation and therefore not contained in the reference list.
When using the numbering or Vancouver system for recording references if you refer to the same book or article many times the reference list becomes very lengthy. If an examiner wants to check your sources of information to verify the quality and quantity of your literature review; this is very difficult to achieve from the reference list because of the multiple listings of the same sources.
Further information on referencing techniques can be found under the Operation and Regs section of this site - specifically in the Quality of Written Work part.
If you wish to include some of you own work, previously submitted for a Post Module Assignment, you can but it must be correctly referenced. If you do not reference it, it will be seen as plagiarised; a special form of plagiarism known as Auto-plagiarism, but never the less plagiarism. For further information see Work Previously Written by yourself and for the correct method of referencing your work please see Plato.