BBC story : “You would have heard about Royal Mail online postage service .
Customers pay for postage by credit card over the internet for first-class, second-class, recorded, special and international deliveries.
Each item of mail is given a barcode, printed off at home, and regular mail can then be posted in a post box.
But recorded and special delivery items must still be taken to a Post Office.”
So you will only save time if you are sending ordinary posts. I think the system still far from mass usage (read corporate, also primarily small business) unless there are ways to avoid going to post office even for recorded and special delivery items.