Hi Mark,
my apologies for the late reply this time. Thank you for that, it's now working perfectly.
In the certificate.php file in the mod/certificate/type/your-type-name folder' I added:
$currentgroup=get_current_group($course->id);
$group = $DB->get_record('groups', array('id' => $currentgroup));
$groupname=$group->name;
around line 80 and then added:
certificate_print_text($pdf, $x + 80, $y + 90, 'L', 'Helvetica', '', 12, utf8_decode($groupname));
on line 104.
best wishes
Grant