From memory there are eight flying Spitfires at Duxford (2 x Mark V, Mark IX, Tr9, Mark XIV, 2 x Mark XVI and a Mark XVIII) and two Hurricanes. You may be lucky enough to see one flying when you visit - especially at a weekend, when they very often have a short display in the afternoon or fly off to display at an airshow.
We had a Spitfire and Hurricane fly in to North Weald yesterday afternoon after they had displayed at Woodchurch. Those two are based at Breighton in Yorkshire.
Next weekend, 7-8 August there is an airshow at Chailey in East Sussex, where several Spitfires are due to fly (some based at Duxford)..
http://www.spitfireart.com/html/chaileyairshow.html
Here are a couple of Duxford residents.
ML407 shot down the first German aircraft on D-Day and was converted to a Tr9 after the war. It is possible to arrange a flight in this one, but there is a three year waiting llist! I am lucky enough to have 37 minutes in my Log Book.
BM597 is a Mark V in the markings of a Polish squadron.
RD