Last week I started a trip on the London LOOP from Erith to Fulwell.
It is a route that brings you through a variety of forest, field, suburb, small town and industrial areas. It a bit difficult to navigate, but with the book (2017, Colin Saunders), sign posting and a GPS on my phone I managed - although with many errors and diversions.
The book gives you step by step directions and many interesting informationa bout the area you walk through. I can't remember directions for 20 km and I don't want to walk with my nose in a book, so I mainly used it for planning.
The sign posting is good, but lacking in places. Many times I had no idea where the route was, but had to relay on the GPS.
GPS: I used OutdoorActive and route which covered the entire route. Many places the GPS-route and the Sign-route differed and in each case I had to select which one to use. Mostly I went with the sign-route, but the GPS was always my Plan B.
I stayed the whole week in Peckham and went by public transport to the days start point and back from the days end point (= next days start point). The advantage of this plan over a traditional walk from point to point is that I had flexibility to decide when I was tired and return next day. Some days I miscalculated and stopped - only to find that the nearest bus stop was a mile away. I learned to check for transportation (Google Maps) when I started getting tired :-)
I plan to finish the route before I turn 75 and then I will take the Capital Ring.
It is highly recommended for people who wants to see London from a new POV. Not only do you get to see wonderful natural areas, but (depending on where you stay) also nw areas of London it self. E.g. I had never been to Peckham before, now I got to shop ( I stayed in an apartment) and use local transport.