Many good suggestions from all of you. At the moment I think I'll take the 17-40 for static aircraft, 70-200 for the Red Arrows where you need a slightly wider field of view and the 300/1.4TC for everything else. I don't think I'll take a monopod as it's just something else to carry and might be too restrictive for panning quickly (though will change my mind a few times between now and 3 weeks time!).
If any of you are interested in well shot, detailed/abstract images of a variety of aircraft I can highly recommend "In Plane View: Abstractions of Flight" by Caroline Russo. Top quality images that will give you plenty inspiration for shots that you may never otherwise think of.
Keep those airshow shots coming!