For Royal Mail Tracked 24 or 48 orders you will receive an email with a tracking link once your order has dispatched.
The tracking link will take you directly to the Royal Mail website, however, the tracker may state:
"Sorry, we're currently unable to confirm the status of your item with reference TK*********GB . Please try again tomorrow."
This can happen after your order has been packaged, and a delivery tracking number has been created for the shipment.
However, it is likely that the package may not have been handed over to the Royal Mail as yet, or it may have been collected by the driver but the package is still on its way to the distribution hub (to be scanned in).
Once the Royal Mail receive the item, they'll update the status of the delivery in Track your item.