You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <backlinks blcontinue="0|Main_Page|3990" />
  </query-continue>
  <query>
    <backlinks>
      <bl pageid="988" ns="0" title="London Tier2" />
      <bl pageid="3487" ns="0" title="CERN@school" />
      <bl pageid="3741" ns="0" title="Grid Storage" />
      <bl pageid="3980" ns="0" title="GridPP - Start Here" />
      <bl pageid="3981" ns="0" title="Start Here - I have a grid certificate" />
      <bl pageid="3982" ns="0" title="Start Here - Installing your certificate in your browser" />
      <bl pageid="3983" ns="0" title="Start Here - is your user community represented by a Virtual Organisation" />
      <bl pageid="3984" ns="0" title="Start Here - I do not have a grid certificate" />
      <bl pageid="3985" ns="0" title="Start Here - Getting a grid certificate from outside of the UK" />
      <bl pageid="3989" ns="0" title="Start Here - Getting a grid certificate from the UKCA" />
    </backlinks>
  </query>
</api>