The CG 300 is a bootiful ride, and really not very hard, despite the AAA point! I reckon it's easier than the Dean.
Phil's Upper Thames 200 could be DIY-ified (it goes right round Oxford, so you must be somewhere on route if you are "near Oxford" ).
The Heart-of-England 300 is very nice AND easy, and could be permified (it passes through Woodstock).