Length: 15½ km (9.6 miles). Toughness: 2/10
Meet up for a 10:45 start in the ticket hall of Wimbledon station (in TfL Zone 3). It's the terminus of one of the branches of the District line and also has frequent suburban services from Waterloo; if coming this way take a train no later than the 10:27 on the Kingston Loop line, arriving at 10:43.
You can return from either Putney mainline station (Zones 2/3; six trains an hour to Waterloo, but not evenly spaced out) or Putney Bridge (Zone 2) on the Wimbledon branch of the District line. For a shorter walk you could drop out after 11½ km at Barnes Bridge station (Zone 3), but there are replacement buses on this branch line and you might prefer to find your way to Barnes station, a short distance off-route.
Anyone wanting a shorter walk with a late start on this Bank Holiday might like to try this meander through various parks and commons in south-west London, with stretches alongside Beverley Brook and the River Thames. Although suburban walks aren't usually too muddy, be prepared for a gloopy stretch alongside the brook in Wimbledon Common.
The walk route has been tweaked to go past several pubs in Barnes but you might prefer to break earlier at the Roehampton Gate café in Richmond Park, where there are also lots of picnic tables. At journey's end there are several refreshment places near Putney Bridge, with a Wetherspoon's on the riverfront being the favoured watering-hole on other SWC walks ending there.
You'll need to bring the directions from the L=swc.391 page.