Thanks Ray
Have figured out how to do this with google analytics:
in the opening <form> add an onsubmit
onsubmit ="ga('send', 'event', 'Contact Form','Submitted');"
where 'Contact Form' is the category and 'Submitted' is the event (and these can be named whatever you want) so that your opening <form> looks like this
<form id="ContactForm" class="form-container" name="ContactForm" method="post" action="<?php echo (htmlentities($_SERVER["PHP_SELF"], ENT_QUOTES)); ?>" onsubmit ="ga('send', 'event', 'Contact Form','Submitted');">
Resource used was https://goo.gl/8NDM1 and https://goo.gl/upzf1N
