shortest is down old street /clerkenwell rd / theobalds road, do the holborn shuffle, down shaftesbury ave, up jermyn street, picadilly, through the underpass and down kensington gore into hammersmith, through chiswick and then over the roundabout to kew bridge.
instead of shaftesbury ave we could do oxford street and through hyde park - both are crappy and full of pissed tourists stepping into the road, and you have the choice of hyde park corner or marble arch to get killed by fast moving traffic. There isn't really a nice safe way to get past park lane.
thats the route baby!