• Both - I used to do that and my (not ideal) route was this:

    Balham
    Clapham South
    Across Clapham Comon to the top of Cedars Road
    Down Cedars then right onto Wandsworth Road
    Up to Vauxhall
    Across at Vauxhall and follow river southside to Westminster Bridge
    Right onto whatever the road's called that runs north along the river
    Left up Northumberland Ave. to Traf. Sq.
    Up Charing X Rd
    Illegal right turn onto Shaftesbury
    Back roads up to the bit of UCL near KX, passing Russel Square

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