Think I sorted it, the double lock is only meant to be activated by the key inside the door. The deadlock is automatic with the smaller “bolt” being pressed in when the door closes.:)
Everything is ok with the normal latch movement with door open or closed. The only way to engage the nightlatch is with the key from inside i.e. when going out lock from inside with key while door is open and then pull closed from outside.
I have a Yale-P-1-BLX-PB-60-Locking-Nightlatch. The latch can be “double locked” from the inside using the key. When leaving the house I used to be able to engage the double lock from the outside by inserting and turning the key once the door was closed, but now the key only opens the door from...