Wordpress - BuddyPress: Adding a new tab in groups

There's an example of this on the buddypress forums which is a good place to start looking for answers.

http://buddypress.org/community/groups/creating-extending/forum/topic/can-someone-explain-how-to-add-tabs-to-the-profile-page/

For the sake of answering here though here goes:

bp_core_new_subnav_item( array(
   'name' => 'My Group Page',
   'slug' => 'my-group-page',
   'parent_url' => $bp->loggedin_user->domain . $bp->groups->slug . '/',
   'parent_slug' => $bp->groups->slug,
   'screen_function' => 'my_groups_page_function_to_show_screen',
   'position' => 40 ) );

And the screen function to render the page:

function my_groups_page_function_to_show_screen() {

    //add title and content here - last is to call the members plugin.php template
    add_action( 'bp_template_title', 'my_groups_page_function_to_show_screen_title' );
    add_action( 'bp_template_content', 'my_groups_page_function_to_show_screen_content' );
    bp_core_load_template( apply_filters( 'bp_core_template_plugin', 'members/single/plugins' ) );
}

    function my_groups_page_function_to_show_screen_title() {
        echo 'My Page Title';
    }
    function my_groups_page_function_to_show_screen_content() { 

        // page content goes here

    }