Following on from this, I found that you need a function for using sub_fields in meta_query
function my_posts_where( $where ) {
$where = str_replace("meta_key = 'driverresults_%", "meta_key LIKE 'driverresults_%", $where);
return $where;
}
add_filter('posts_where', 'my_posts_where');
Hope this helps someone else!