Despite its size, the Watson series is not intended to be comprehensive. I don't know much about the essential series, but the London is a very small part of the opening world and it is not likely to get much attention in general works. For a London introduction, you may want to try First Steps: the Colle and London Systems.
https://www.chess.com/article/view/how-to-understand-openings
I wonder why London system not mentioned in openings books
I have Watson series and the essential series and i could not find London system
Does it have another name ?
Or the openings systems have other sources to read about them ?
I am a beginner and probably my knowledge not helping me to find the answer
If the systems have their own books what do you recommend?