Lawton is legit as far as practical permaculture goes [as opposed to hippy-dippy ‘bio-dynamics’].
His focus is tropical/ sub-tropical environments, but does teach the whole set of permaculture principles.
Permaculture originated with Bill Mollison and David Homlgren. They are the other two names you should look for in a genuinely useful book on permaculture design.
Permaculture as a system of design for food production is sound, but most specifically if you have some acreage to play with. It looks at the sucessful self-sustaining environments in your geographical location and then attempts to recreate an ecosystem where each ecological niche is occupied by a species of your choosing [i.e. those that are useful to you].
It is also neat in that it tries to close nutrient loops; feeding what is considered ‘waste’ one area to another purpose on your property. [e.g. you don’t have too many snails, you have an absence of ducks in your system etc]
Many versions also look at plants that build fertility by ‘mining’ deeper land for essential minerals [like comfrey for example], or those that can fix and then release atmospheric nitrogen [like lupines, acacias, and other legumes].
The other thing that it does have going for it is that it actively builds the topsoil layer and the health of the ecosystem, rather than stripping the nutrients from the soil, washing them through, and degrading and eroding the topsoil layer as much modern agriculture does [through the necessity of producing bulk staples for 1000’s based on the labor of just a few].
It is not a Panacea to solving the problem of food production for 7billion+ people, but it is effective if designed well and used effectively. IMHO it would work to a village scale 2-400 people. But by it’s nature it is not the kind of system that is intensive enough to provide for a city of 2-4 million+ [assuming you planted the city’s hinterland in this way.
Hope i didn’t hit too much of a tangent there!