I?ve commuted by bike from ED to Leatherhead for the last 4 years or so. Yet to find a really good route... I tend to go Tulse Hill, Streatham, Mitcham, Rose Hill, Sutton, Cheam, Epsom. I get off the South Circular asap after Tulse Hill and use back roads (Hillside Rd and Amesbury Ave) to Streatham High Rd. Then A216 and A217 to Mitcham then keep on London Road to Rose Hill to Sutton. Reasonably quiet route from Sutton (I head up the High Street and then right at the rail station (mulgrave road)to East Ewell along Sandy Lane and Northey Ave. Then you are onto the A24 to Epsom. It is reasonably hilly and otherwise busy with traffic and there are lots of traffic lights.