I've now tried the hard reset Orange suggested, entered my Google account details, and the GMail app is still not there. So I'm no further foward, and I've lost all my settings etc...
This is consistent with your conclusion that the applications are completely missing, despite my Orange contact saying
"The Gmail application is core to the Android Operating System being used on this phone, it can only be bypassed by user error."
!!
Grr. Back to Orange.
PS thanks for your instructions -- I'm going to pursue Orange a bit more before trying them though!