Thanks Jason, great idea & beautifully simple too.
I've been manually editing changes, but at least I now thoroughly understand the code.
Yep, I think that's more or less it Bill.
Minor point, the flow needs re-ordering, you need to create the page before you can create the email, so...
Create the new database column
Create a new page
Add a database connection, just copy & paste it from your confirm page, it will look like: <?php require_once('Connections/YOURCONNECTION.php'); ?>
Copy & paste my code onto your page (update $YOUR_CONNECTION)
Create the email
wrap the email with the if statement
Tell WorldPay your "Payment Response URL" and check the "Payment Response enabled?" box
Once happy, copy test configuration to the live environment on WorldPay