Oops -  I just read the second line of the bit I quoted properly , so I guess the satchel isn't the go and it will probably be over 500gm? You can still just purchase and print an express post label via eBay or C&S, though. I do that sometimes, and the staff at the PO just put some yellow 'express post' tape on it to help show it is express, since I print the labels in greyscale.