Ok, so this is a slightly strange request but my clients have asked me to put in some ads that appear to the side of the drop down menu text... I have had a quick couple of searches of plug ins but can't find anything suitable for this. Any suggestions? Or what alternatives would you suggest? It's a tourist website that also sell advertising space to local businesses and vacation rentals

Is it for a wordpress site? If so you just need add the code to menu.php.

Create a conditional and use this: https://codex.wordpress.org/Function_Reference/wp_page_menu