Using you example texts
Search for
Code:
</p>(.)(.) <p class="calibre1">([a-z])
and replace with
The \3 means to replace with the 3rd stored value from the search
which will be the lowercase letter at the beginning of the new paragraph.
(The reason I also store the two newlines is that I have a very similar one, and use this to differentiate between my two search values and then have a different replace value.)