DBS eSource contains dissertations from DBS students with a mark of 1.1 or above.
Some dissertations (usually only older ones) may be marked as restricted access. This means they can be accessed online only when on-campus.
EThOS eThesis Online Service (British Library)
Limit search to items available for immediate download from EThOS or the Institution (over 380,000 theses). 
Access to the full-text of a large and growing number of theses from over 579 universities in 29 European countries.
You should not over rely on dissertations as the primary sources for your academic work. They should be cited alongside more scholarly sources to ensure you produce high quality academic work.