Yes you can given that you pack them properly and take care that they cannot cut their way out of the packaging. The following is taken from the Royal Mail website...
Sharp objects (including knives, kitchen utensils and gardening tools)
International & UK - Allowed in the mail, see packaging guidelines below:
Sharp objects like knives*, kitchen utensils and gardening tools may only be posted if they are packaged appropriately so that they are no risk to employees, other postal items or recipients.
*Excludes knives that are banned under UK laws - see Weapons
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. 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.