Missing Key on UK PowerBook 12 inch Aluminium

I just acquired a mac powerbook 12 inch G4 aluminium, but it has a missing key. Its between the shift key and the Z key. I'm in the UK.

Every picture I look at has the shift key twice as wide and covering the spot where this key is.

Does anyone know what key it is? I've tried pressing it, but it doesn't seem to do anything on the screen. Doesn't type any symbols, and doesn't work like the shift key.

Please help so that I can order a replacement key. Thanks

Could it be the Tilde key? I notice now that there doesn't seem to be one anywhere else on the keyboard.