Thanks for the help @hube2
To make sure I wasn’t getting empty results, I changed the ACF to relationship and used;
<?php $locations = get_field('development_plots'); ?>
<?php if( $locations ): ?>
<?php foreach( $locations as $location ): ?>
<span class="accent_color"><?php echo get_the_title( $location->ID ); ?></span>,
<?php endforeach; ?>
<?php endif; ?>
To output them, which they are but obviously want the last one to have ‘and’ at the end.
I tried the above, but that just blew it up again…