Ok, I avoided the pitfall of many an airtight builder by planning to have a doorbell.
Now we're trying to fit the push and are struggling (hasten to add it was chosen by the mrs).
It'a a flush stainless steel plate with two fixings that have a machined thread on one side (to mate with the push) and a screw on the other (to fix to wall).
Problem is that once the fixing is attached to the push, there is no way to rotate the screw, unless you rotate the whole push which obviously doesn't work.
Have spoken to the Portuguese manufacturer but they just sent me the technical drawing, not any instructions.
Wondering if there is a special plug that can hold the screw without it rotating (I.e.) just pushing it in.
Not keen to just bond it, would like to solve the puzzle!