i have tried this and works fine with mine. you may view on the top in header.
{if $login eq "" }
<a href="<A href="https://www.lootsale.co.uk/error_message.php?need_login">Login/Register</a>
{else}
<a href="<A href="http://www.lootsale.co.uk/include/login.php?mode=logout&redirect=customer">Logout</a>
{/if}
Best Wishes..