after login return to previous page

I already have a check if logged in script working well, I need it to return the user to the page they where on before they where sent to the login page.

$html .= '<p>' . __('', 'cubepm') . '<a>' . __('<img src="/hireme/wp-content/uploads/2012/10/login.png" alt="log in to send message">') . ' »</a></p>';
	}

[Moderator Note: Please post code or markup snippets between backticks or use the code button. As it stands, your code may now have been permanently damaged/corrupted by the forum’s parser.]

This is the current output for users not logged in, how can I change it to redirect back to the previous page?