Do many people cycle back from the London to Brighton,

[Wally]

or are the roads empty of cyclists?

 

[Old Walrus]

Some brave souls do! The very brave use the A23 out of Brighton and get stuck on the central reservation due to the road configuration......ouch! (cycle path parallels the A23 for the more prudent)

 

[BentMikey]

There were loads of people cycling back this year, there are several possible routes back. Assuming I get over my lurgy I'm planning to ride back next weekend after riding down with the old cars.