Navigation to show sub levels if in parent

I almost have what I need but am struggling with the final part. Here’s what I need.

My website has three levels deep

Page 1
Sub page 1
Sub page 2
Page 2
Page 3
Sub page 1
Sub page 2
Sub sub page 1
Sub sub page 2
Page 4

So, if the user is on a top level page they see other top levels and the child pages i.e. page 1, they see

Page 1
Sub page 1
Sub page 2
Page 2
Page 3
Page 4

If they are page 3 sub sub page 1;

Page 1
Page 2
Page 3
Sub page 1
Sub page 2
Sub sub page 1
Sub sub page 2
Page 4

This is working on all levels apart from sub sub pages which only sees the top level pages. It should see the final example above but it is showing

Page 1
Page 2
Page 3
Page 4

Here’s the code

<ul>
<?php
$Pages = wp_list_pages('title_li=&echo=0&depth=1');
$InnerPages = wp_list_pages('child_of='.($post->post_parent != false ? $post->post_parent : $post->ID).'&title_li=&echo=0');
$Title = ($post->post_parent != false) ? trim(get_the_title($post->post_parent)) : trim(wp_title('', false));
if($Title != '')
$Pages      = str_replace($Title.'</a></li>',
								$Title.'</a>'.
								'<ul>'.$InnerPages.'</ul></li>',
								$Pages);
echo $Pages;
unset($Pages, $InnerPages);
?>
</ul>

Can anyone help?