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>
    <allfileusages gafcontinue="England_riot_map-asva-110823,1.jpg" />
  </query-continue>
  <query>
    <pages>
      <page pageid="17453" ns="6" title="File:Bacibp product.jpg" />
      <page pageid="17624" ns="6" title="File:Britain riots fire-apha-110823.jpg" />
      <page pageid="17626" ns="6" title="File:Britain vandalism-asha-110823,1.jpg" />
      <page pageid="27326" ns="6" title="File:British empire-asha-111229.gif" />
      <page pageid="18139" ns="6" title="File:Bud3.gif" />
      <page pageid="18147" ns="6" title="File:Bvine.gif" />
      <page pageid="27327" ns="6" title="File:Cameron eu europe-apha-111229.jpg" />
      <page pageid="30433" ns="6" title="File:Crashing astroids-apha-101208.jpg" />
      <page pageid="17815" ns="6" title="File:Crwnos product.jpg" />
      <page pageid="17445" ns="6" title="File:Dge product.jpg" />
    </pages>
  </query>
</api>