Going back to the discussion on longer events in Kent. I did a 400 DIY end of September 18 that went south from Hertfordshire, overnight through Woolwich foot tunnel into Kent. Then returned via the Gravesend ferry and Essex the following afternoon. I set off at 7:20pm in the evening and the timings worked really well. So I think if you take in bits of Hertfordshire and Essex and plan an overnight start that passes through east London; an interesting 400 is quite achievable. The roads overnight through east London were pretty quiet but there were plenty of take aways and mini marts open to top up food, drinks.