One route you could consider, it fits your criteria, is the High Weald Trail from Sussex into Kent. Catch a train to Horsham, get off the train and you are on the walk. As it meanders its way through fields, woods, villages and orchards there are numerous opportunities to cut it short (rail stations are often nearby) should you so wish. Or, you could do the whole route to Rye and then catch a train home. The opportunities for wild camping, in my experience, are endless. The villages en route (and pubs) are, again in my view, are some of the best I've come across. If you are also looking for the 'rustic', for culture, middle class values, observing our class system in action, etc, there is something for everyone on this route. Villages like Goudhurst, Cranbrook, Tenterden and of course Rye are as good as you will find anywhere in the UK.