Your details for the checkout are stored by a cookie on your own device Dave. It will be a setting on your device for sure, or if you tried placing your order on a device you've not used to do that before, then it won't have it stored at all.
We'll be doing better than that shortly though, as pretty soon you'll have the ability to register your details as an account, so you'll be able to log on to get your details, and even be able to see your order history I hope.
Watch this space.