creative_lounge on "wp_list_pages Question"

Hi,

I am sure I can't be far off, but for whatever reason I am unable to display child pages of a parent page.

This is the code I am using :

<?php global $post; ?>
<?php wp_list_pages('title_li=&child_of='. $post->ID .''); ?>

I am using global $post as it is outside the loop. I am wanting to use best practice of using a dynamic page ID. BTW If I do pipe through the ID manually it does work, so it is clearly my code relating to the page ID.
I have tried and searched and now require some help to point me in the right direction.

Thank you in advance,