pwaring, 
Don't think I'll ever buy something that needs assembly from Argos again. Part was missing when I opened the box.
Online order of spare parts: Not available for this item (it doesn't have a part number).
Online chat: We can't do anything, call the store.
Call store: Always busy so you get redirected to the overflow call centre... who can't do anything.
Visit store: TODO
IKEA OTOH: 6 digit code for each part, order online, posted immediately free of charge, no quibble.
