I recently purchased a 2015 Mondeo trend diesel wagon which is supposed to have Lane keeping aid. I have set the menu at different times to each of the three possibilities being  alert+aid and also aid and also alert separately. When in alert it seems to work fine giving me a wheel shaking Rumble immediately when I cross any detected lines without an indicator. When I put the system in aid+ alert there is certainly no steering assistance back into a Lane when a line is crossed and furthermore even the aid doesn't seem to work properly anymore as it only rumbles the wheel when I am already halfway in the next Lane rather than when I am Crossing the Line. Does this system ever work properly or have I bought a dud car that needs some component replaced?

It's a very subtle assistance, basically if your turning the wheel to make it work it won't respond or you would be constantly battling against it. 

The ideas is slight resistance is felt by you holding steering ( so it won't work also with no hands) so you not inputting any turning force as such or very minimal. Then as long as the camera is detecting both the nearside and centre makings  the system will pull the steering slightly back in .