My favorite regional walking guides are the Pathfinder Guides. They have a book for nearly every part of the UK. The also have a "Short Walks" series. You will find them in most big bookstores. They have good walk descriptions and use the Ordnance Survey maps in the books, but it is always good to purchase the full map as well.
Pathfinder Peak District: Walks: The best short, medium and long country walks in the Peak District National Park... by Crimson Publishing (1 Nov 2009)
Peak District: Short Walks
AA (Automobile Association) also publish walking guides for many regions (their maps are not as good). And there are online resources.
We have not been in the Peak District recently, but are planning a trip this year. I read about a walking trail along a disused railway line that sounds interesting.
October will be getting colder and wetter, but there will be many good days.
Another area to consider is the Southwest - Dorset, Devon, Cornwall. The South Coast Trail goes along the coast starting in North Devon, around Cornwall, South Devon, ending in Dorset. We have hiked several stretches of it.
This is always my dilemma too - do we travel in England because we are here and it is cheaper because we don't have to fly or train somewhere and we have our car? Or do we take advantage of how easy it is to get to continental Europe? We try to do a combination - but I have seen more of France in the past four years than I have other parts of England.
