I bought several mortice latches from Homebase and they look like your standard type with regard to dimensions and operation. however I also bought two different styles of mortice knob to go with them and in each case when you attempt to screw the knob surround to the door it fouls on the mortice latch. It seems to me you would need a door about 70mm thick for knobs tofit. Handles are not a problem as the fixing hole dimensions for these fall outside the footprint of the mortice latch. Has anyone else had this problem. It seems to me that all mortice knob fixing screws are going to foul the latch but there are plenty out there for sale so am I missing something?