I had the same problem with my escort van.
if you look to where your right knee would sit whilst driving you`ll see the fuse box under the dash.behind the fuses are some black boxes,(im not sure what they are but their electrical self contained units approx 1"x1")these boxes just work themselves loose and break the electrical chain from the ignition to the starter motor.
just literally push them back in place and try the key.
i only found this out from the AA man when he came to fix it for me.
i still have it work loose sometimes but i have the knack of banging it in the correct place!!
hope this helps?
lee nettleton
July 2008