I now have group info showing in my main events list. I did this by creating a new placeholder file called groupinfo.php and saving it to my-theme/plugins/events-manager/placeholders/ containing the snippet of code agelonwl kindly pasted above. I also changed both instances of $event to $EM_Event
I added my placeholder #_GROUPINFO to the core file plugins/events-manager/classes/em-event.php like this:
$template = em_locate_template('placeholders/groupcolumn.php', true, array('EM_Event'=>$this));
$replace = ob_get_clean();
Then put my place holder in the correct place in Default event list format in the back end and all is tickety boo.. well nearly.
I am sure this is far from ideal as I don't really know what I am doing with php or the core files and of course this will need replacing after every update but aside from this, the only issue now for me is not being able to search groups via the search form. If I can do that then at least I'll have my site working as intended even if it is a bit weird.
Any comments, advice or pointers appreciated as always.