Return to where you got them from, especially if from the NHS.
Wheels for the World, part of Christian charity Through the Roof, accepts crutches and walking sticks, as well as used manual wheelchairs, for refurbishment and distribution to people in need in Africa. Contact 01372 749955; email email@example.com (Currently based near Salisbury, but moving to Aldershot)
Disabled gear.com has details about buying and selling crutches and other walking aids, as well as manual and power wheelchairs and has links to many charities that accept used wheelchairs and other mobility aids.
If in poor condition, take to Marlborough Household Recycling Centre and ask where to put them.