London to Edinburgh for charity

can anyone help, the other day in the pub i told everyone i was going to ride to edinburgh from london to raise money for my mate who has ms. now even though it was pub talk i'm gonna do it cos my mate needs money for a new electric wheel chair, so by hook or by crook i'm going to do it. now heres where i need your help i'm 36 reasonbly fit (the most i've ever cycle in one day is 40 miles). but i'm not an experienced cyclist, i've pottered about in town but never took to the open roads on a proper road bike. so could anyone please tell me how to train for something like this ( iwant to do it in about 5 days) and a route to take avoiding the A1

cheers

Jamie