Thank you Le P.
I have tried deleting all the Bluetooth paired items both on the Alcatel and the K480 - same result. Similarly with all three channels on the 480, plus the same result on a further single channel Bluetooth keyboard. Both the keyboards work perfectly with other phones, so the problem would appear to be solely with the Alcatel. Having said which, the basic pairing process proceeds satisfactorily (keyboard is recognised and a pairing code is generated) but instantly changes to disconnect once the pairing is complete - puzzling and quite irritating
I have, also, reset the Alcatel to original factory settings - still no joy. The joys of electronic wizardry!
The second button is to accomodate Apple software as distinct from Android.