Peter HS said:the world's biggest parking lot - the M25. Then I need a machete to hack my way through the traffic from the parking lot to Walthamstow.
Don't go on a Friday, traffic is worse. Also leave after 9am
Also.. there are already more than enough matchetes in Walthamstow to go around!!
Try http://routes.tomtom.com to plan you route just before you go, as it will take into account live traffic.. unless of course you have a GPS with inbuilt traffic receiver.
Trust me, my family and I are from near Gatwick, and I have done this route too many times to remember