Thank you all for your examples, this one made me smile. - I don't have the time to explain it to you - Je n'ai pas le temps de te l'expliquer.
I am afraid that even with the examples the rule(s) still goes straight over the top of my head and if I try to construct a sentence using it I just get a mental blockage.
I am hugely encouraged to realise that pretty much all the examples I have used and do use on a daily basis without error, just from absorbtion.
If I am aware that I have a problem with something then I become very self conscious and the problem gets much worse, the mental block again, ignorance can indeed be bliss and had enabled me to get thus far, I only recently started using "en" in speeech after hearing it all the time and gaining the confidence to use it in sentences, I cant say that I really thought about the construction of the sentences containing it, they just sort of started of their own accord.
Because I have so little daily social contact with people and virtually none at all during any school holidays I would say that 98% of my learning comes from watching the television, it amazes me when I analyse that I must sub-consciously block out what doesnt make sense to follow what does, for example a year ago I would have said I understand 100% of what I heard yet only recently did "en" make it through this filter to my consciousness, clearly it has always been in the paroles.
It gives me confidence to know that aside from falling into habits of bad speech, and I do hear a lot around here, I will carry on learning by absorbtion, after all I dont know any of these rules in the English language (dont understand would be more accurate).