[LARdT]

IF you have

<div class="calibre10">
   M
 </div>

 <p>y jailers merely tightened their hold and frog-marched me when I wobbled. Suckers are very strong; they may not have noticed that they were now bearing nearly all my weight as my knees gave and my feet lost their purchase on the ragged ground.</p>

and you want to end with something like:

<div class="calibre10">
   <p>My jailers merely tightened their hold and frog-marched me when I wobbled. Suckers are very strong; they may not have noticed that they were now bearing nearly all my weight as my knees gave and my feet lost their purchase on the ragged ground.</p>
<div>

Your SEARCH string is:

<div class="calibre10">(\n\s*)([([\(\ÑñÓ/ÃÁÉÍÚáéíóúÜü¡!?¿*:«»"'-%…=–º©—“”#{(¼)\).,;a-zA-Z0-9\-_\s\c]*)(\n\s*)</div>(\n\s*)<p>([\(\ÑñÓ/ÃÁÉÍÚáéíóúÜü¡!?¿*:«»"'-%…=–º©—“”#{(¼)\).,;a-zA-Z0-9\-_\s\c\<\>\[\]\n]*)</p>

and replace string is: (you may copy the carriage returns inside SIGIL replace box)

<div class="calibre10">
   </p>\5</p>
<div>

You have plenty examples of RegEx and explanations about them in

http://mipapyreebookreader.blogspot....ch/label/RegEx