The other thing that you can do is just unplug the phone from the socket. I have tried this and what happens is that the line just rings and rings, ie caller hears ring tone but there is no sound in the house. I am not certain that this still works but I have done it in the past (around 10 years ago)
Ok, thanks all.
Reason being, apparently, friend apparently never uses phone (is that poss?) but needs line for puter.
There is no button on the base for switching it off but I googled the model number and we seemed to achieved what was wanted. If not we will, as woolfgang says, just unplug it.
Watch this space!!
Once again, thanks all.