Regular Countryside Rides from Upminster (every Sunday except Christmas Day)

Havering CTC: Countryside rides every Sunday from Upminster, very easy to get to from Barking by c2c train - check they're running though.

Also on the first Sunday of each month they have a short, all-comers ride, more geared towards newer cyclists.

http://www.haveringcycling.com - for full details.