Add Categories without post

Use the template tag, wp_list_categories() with the hide_empty=0 argument:

<?php
wp_list_categories('hide_empty=0');
?>

If necessary, consider downloading and installing Otto’s PHP Code Widget then put that code in one of those widgets.

Related:
Stepping Into Template Tags
Stepping Into Templates
Template Hierarchy

Thank you Micheal, but perhaps i have not made myself clear. If you take a look at this page https://www.norwichcitycentre.com/advertise-with-us/home-page-feature/ you will see that the category does not display because I have not assigned a post to this category. I have infact inserted copy using php else in the archive.php, this copy will only show if I also include a post, trouble is that I do not want to add any posts to this category.

A simple way round would be to use this category as a page but this would totaly mess up my structure!

Any other suggestions?

Don’t think that will work without having a least one post in the category. Sorry.