An update:

When I look at the php file that Xara has generated and that is on the server, the desktop variant has in it:

<div class="xr_noreset " style="position: absolute; left:336px;top:1210px;width:552px;height:236px;">
<?php
require ("configuration.php");

//SET UP SOME PARAMETERS FOR THE USAGE OF THIS CODE
$tt=0; //we want non-teacher-training courses here
$orderBy="ORDER BY Location_name, Start_date ASC";
$reqLevel="Level 1 - Being Present";

include 'functions.php';

displaySimpleCourseList($tt, $orderBy, $reqLevel);

?>
</div>

and this in the mobile variant of the same file:

<div class="xr_group">
<span class="xr_rn_ xr_ar" style="left:20px;top:1393px;width:439px;height:263 px; background:url('index_htm_files/1665.png') 0px 0px no-repeat; background-size: 439px 263px;"></span>
</div>

Surely this is a Xara bug? Xara has generated a .png file for the php in the placeholder of the mobile variant, which the server can never interpret as php!

Best wishes,
Heather