Show Description Field on Individual Webform Submission Result
After looking through the webform module I found out how to achieve this.

I used hook_webform_component_display_alter() which is there to enable customising the display of components in display only contexts. This function is in webform.api.php. I created my own function using this hook in a custom module to add the description to all textfield components as follows:

&lt;?php
function my_mod_webform_component_display_alter(array &amp;$element, array &amp;$component) {
  if ($component['type'] == 'textfield') {
    $element['#description'] = $component['extra']['description'];
  }
}


For reference, the notes and example given from the webform module for hook_webform_component_display_alter() are:

/**
 * Allow modules to modify a "display only" webform component.
 *
 * @param array $element
 *   The display element as returned by _webform_display_component().
 * @param array $component
 *   A Webform component array.
 *
 * @see _webform_display_component()
 */
function hook_webform_component_display_alter(array &amp;$element, array &amp;$component) {
  if ($component['cid'] == 10) {
    $element['#title'] = 'My custom title';
    $element['#default_value'] = 42;
  }
}