You can either go up the river to Southease then follow the south downs way most of the way, or out through the back of peacehaven and past the back of woodingdean. Think it's 12 miles via the first route and ten via the second. You can plot routes on http://maps.the-hug.net/ and itll give you a distance and profile.
Thanks, sounds like a decent walk but I will stick to walking to the station now, stopping at the cafe and the Railway Club.
I think the stairs to the WSU would finish me off after walking 10 or 12 miles.