PHP soap and namespaces. PHP Fatal error: Class 'Jira\SoapClient' not found

We are updating our codebase to use the namespace functionality provided in PHP-5.3+

Previously, our files all lived happily on the webserver in /htdocs/php but now we are separating our scripts, and putting our PHP libraries in /htdocs/php/lib/

In /htdocs/php/lib/ we have a file called Jira.php which we have given a namespace to:

<?php
# Define a namespace for this library
namespace Jira;

function create_client($jira_url, $options)
{
    global $client;

    try
    {
            $client = new SoapClient($jira_url, $options);
    }
    catch (Exception $error)
    {
            echo $error -> getMessage() . "<br/><p style='color:red'> Could not connect to Jira </p>";
    }
}
?>

However, when we try and call this function from a script in /htdocs/php, we are getting the class not found error:

PHP Fatal error:  Class 'Jira\SoapClient' not found

This is failing when we try creating the SoapClient object.

I have verified that I have the php-soap package installed in /usr/share/php/SOAP/ and php_info(); is showing that it is enabled etc.

So presumably this is a problem with the namespace convention. How do we include that class without it throwing an error?

Regards, ns