Clarify the postage due on a postal tube
Tubes can be a maximum of 90cm long and length plus 2x diameter of 104cm, but how do I find out what that costs?
If I go via the button 'Buy online postage' to https://send.royalmail.com/send/youritem?compensation=20&country=GBR&format=SmallParcel&weight=500&weightUnit=G there is no way to find what postage is due on a tube - please try it yourself. It seems to me that there is a missing link.
However, using Get a Price, at https://www.royalmail.com/price-finder, select UK, Parcel, then Medium Parcel, you will see the maximum dimensions of a tube. Therefore tubes within this size should go as medium parcels, so typically £5.90.
So why does your page not show this?