Install latch on door with multi-point lock?

[dagoof]

I moved recently to a house with a solid wood door that has a multi-point lock system, however, we're missing the latch. It's not really practical to key-lock the door from the inside every time you come in the house.

I wanted to fit a yale-type latch but I'm guessing there's lever in the frame for the multi-point system - the width of the frame (before it gets to the window) is only about 100mm.

I know, even a snib could be used but my wife's not the best with security What are my options?

 

[JohnD]

Has it got a Eurocylinder?

Photos of the face and edge of the door, and the key, and brand names, will all help.