Never led a walk before? Perfect! This is a great opportunity to give it a whirl.
Don't know where to go or unsure of navigational ability? No problem!
How about the Thames path?
You will be following a big river so getting lost is not an option. Here are the route descriptions for the various stages:
Or the Lee Valley walk?
You are following a different river/canal so ditto. Here are the route descriptions for the various stages:
Don't like walks following water?
How about the Green Chain (a waymarked route for the hills, fields commons, parks, woods, and other open spaces in SE London). As some of these sections are fairly short, you may need to string a couple together.
Other suggestions can be found at https://tfl.gov.uk/modes/
Our links page contains yet more links to different websites with walk descriptions/ideas