Many timber sash & case windows are only locked or held shut by centre fasteners of the type shown.
These can easily be flipped or forced open, as the fixing screws are limited by the size of the window frame.
Another means of securing these windows is to use Dual Screws.
Some Dual Screws are typically only 70mm long and Edinburgh Sash & Case window frames are typically 60mm thick, so only 10mm of dual screw is holding the two parts together. If we fit Dual Screws we use the long-series version which are 100mm long. Dual screws are not always the best to fit as they rely on the sashes meeting evenly when closed to ensure the screws go into the external frame in the middle.
If you are getting window locks fitted to sash & case windows as an alternative we’d suggest Sash Stops which are key operated and don’t rely on the overlap.
A hole is drilled in the window frame and the silver threaded insert is screwed into the hole. This insert remains fitted to the window , by using the supplied keys the brass stop is screwed in and out of this insert. The stop when fitted prevents the top and bottom sashes passing each other and thus the window opening.