A door latch system for installation in a door panel having a crossing-drilling and an edge-hole intersecting the cross-drilling, the door latch system comprising: a. a door latch having a face plate and a body, the body having a body axis and including an operation aperture at a desired backset from the face plate, the operation aperture being arranged for rotation in the body about an operation axis orthogonal to said body axis; b. an adaptor to receive the door latch body; c. two handles (62A,B), each comprising a rose base (60A,B) and lever or knob rotatably disposed in the rose base; and d. a handle spindle having a longitudinal axis, wherein: the door latch system is adapted for installation in the door panel by: i) the latch body being configured to be received in the edge-hole with the face plate substantially flush with the edge of the door; ii) the adaptor being configured to fit with a close sliding fit in a door cross-drilling of between 40 and 50 mm, with a passage to receive the latch body so as to support the latch body in the adaptor in the cross-drilling and so as to prevent rotation of the adaptor with respect to the latch body about said operation axis; and iii) the operation aperture and handle spindle being configured so that the handle spindle passes through the operation aperture, whereby said operation axis and longitudinal axis are coincident, and is received in each handle or knob (62A,B), whereby rotation of the handle or knob results in rotation of the operation aperture about said axes and actuation of the latch, and wherein: cross screws are provided to clamp the rose bases together, each rose base comprising screw holes disposed diametrically opposite one another on either side of said lever or knob, and so that said cross screws can be received through said cross-drilling around the latch body and through the adaptor, an extension sleeve of the rose bases around each screw hole supporting said cross screws and engaging the adaptor to locate the rose bases rotationally around said axes with respect to the adaptor, characterised in that said extension sleeves are C-shaped along their section whereby the diameter of the part of the handle to be received in the cross-drilling is defined by a boss centred on said screw holes into which said cross screws are adapted to be screwed. a. a door latch having a face plate and a body, the body having a body axis and including an operation aperture at a desired backset from the face plate, the operation aperture being arranged for rotation in the body about an operation axis orthogonal to said body axis; b. an adaptor to receive the door latch body; c. two handles (62A,B), each comprising a rose base (60A,B) and lever or knob rotatably disposed in the rose base; and d. a handle spindle having a longitudinal axis, wherein: i) the latch body being configured to be received in the edge-hole with the face plate substantially flush with the edge of the door; ii) the adaptor being configured to fit with a close sliding fit in a door cross-drilling of between 40 and 50 mm, with a passage to receive the latch body so as to support the latch body in the adaptor in the cross-drilling and so as to prevent rotation of the adaptor with respect to the latch body about said operation axis; and iii) the operation aperture and handle spindle being configured so that the handle spindle passes through the operation aperture, whereby said operation axis and longitudinal axis are coincident, and is received in each handle or knob (62A,B), whereby rotation of the handle or knob results in rotation of the operation aperture about said axes and actuation of the latch, and wherein: cross screws are provided to clamp the rose bases together, each rose base comprising screw holes disposed diametrically opposite one another on either side of said lever or knob, and so that said cross screws can be received through said cross-drilling around the latch body and through the adaptor, an extension sleeve of the rose bases around each screw hole supporting said cross screws and engaging the adaptor to locate the rose bases rotationally around said axes with respect to the adaptor, characterised in that said extension sleeves are C-shaped along their section whereby the diameter of the part of the handle to be received in the cross-drilling is defined by a boss centred on said screw holes into which said cross screws are adapted to be screwed. cross screws are provided to clamp the rose bases together, each rose base comprising screw holes disposed diametrically opposite one another on either side of said lever or knob, and so that said cross screws can be received through said cross-drilling around the latch body and through the adaptor, an extension sleeve of the rose bases around each screw hole supporting said cross screws and engaging the adaptor to locate the rose bases rotationally around said axes with respect to the adaptor, characterised in that said extension sleeves are C-shaped along their section whereby the diameter of the part of the handle to be received in the cross-drilling is defined by a boss centred on said screw holes into which said cross screws are adapted to be screwed.