Let me explain to you what they are saying in the following snip from the RM siteYou won't be able to send any bladed article via any RM service. Seems pretty clear.
I have made the relevant section more obvious. You cannot send bladed items through normal postage options but you can through the specific service designed for age restricted items like blades. Just as you cannot send a large package as a small letter you cannot send an age restricted item except by the age verification service.
- UK - Allowed in the mail, with product restrictions and packaging guidelines. IMPORTANT NOTICE: on and from Monday 22 April 2024 Bladed Items will be prohibited by Royal Mail for all UK destinations.
These items may only be sent using the Royal Mail Tracked Age Verification service (this service is only available through Royal Mail Click & Drop
- Package appropriately so items present no risk to employees, other postal items or recipients.
- Wrap heavy cardboard around sharp edges and points, strong enough to ensure that the contents do not pierce the outer packaging.
- Wrap each item with cushioning material and place in a suitable outer container such as a padded envelope.
- The sender's name and return address must be clearly visible on the outer packaging.
- Marked to clearly indicate a bladed item is enclosed
Link to the RM click and collect online booking system showing all the potential options including age verification service. I selected small package at 1kg in the earlier page.