Bit of a trek, but once south of Croydon some lovely countryside. Mostly following National Cycle Routes 21 and 20. More off-road cycle track sections than I had expected, adding interest as well as bumpiness to the route. Finishes with a rather boring, but blessedly flat, stretch of cycle path alongside the A23 into Brighton.
Ride stats
miscellaneous stops)
More detail and a map of the route at GarminConnect

The Rye, Peckham

Was lost then was found - route rediscovered (and lunch stop)

Brighton Train Station
Refreshments
Lunch at The White Bear, Warlingham
References
Downs & Weald Cycle Route: the official route map & guide to the 159 mile cycle route from London to Eastbourne and Hastings, Sustrans
OS Landranger Map 177 East London
OS Landranger Map 187 Dorking & Reigate
OS Landranger Map 198 Brighton & The Downs