I can understand your concerns JT but these two videos contain a locking mechanism for sliding windows that appears to be similar in type to those being installed in FNL’s scheme. They too can be removed and ‘thrown in drawer’ after removal with an Allen key. These types of window limiters appear to be sanctioned by Fair Trading as the videos are on their web site.
I may be wrong but I think that the Office of Fair Trading are more concerned that a child cannot easily remove the lock once it is installed, hence the need for a key or Allen key to remove or override the lock.
https://youtu.be/xLlINRKbnVY?list=UU8O15SNsdBG_suQ0M3oAQkQ
https://youtu.be/5yTUUWp4n3o?list=UU8O15SNsdBG_suQ0M3oAQkQ
It is a bit confusing though.