Most British PhD theses can be requested via the British Library's EThOS service (see link below) so are not requestable via the Inter Library Loan service.

Sourcing thesis not held by Ethos including Masters-level thesis is more difficult as they are seldom held by libraries and, if they are, require the written permission of the author to obtain a copy 

Please see finding dissertations & theses for more information and further sources for locating these.  Some databases such as Proquest contain some UK records. 

Dissertation or Thesis abstract

Abstracts of most theses can be found freely available online so are not requestable via Inter Library Loan.

If the reference is from Dissertation Abstracts then an abstract is all that is available for that reference and not the full text of the dissertation.  

A dissertation abstract or thesis abstract only provides a summary of the whole paper.  It is likely to contain the key information that the research is based on.  For example, the research question or hypothesis, an outline of the methodology used or perhaps key theories relating to the topic.  It may also contain a summary of the findings of or key recommendations arising from the research. 

Theses and Dissertations from abroad

Thesis and Dissertations from other countries are very hard to source. Some are available via Dissertation Express  Anything found via Dissertation Express, you would need to obtain for yourself.