Conti Travelcontacts are good tyres for a trip like that, as are Schwalbe Marathons.I would not be too keen on the Marathon Plus as they are very heavy and have a fair bit of rolling resistance. You don't really need that kind of protection when touring (I feel they are more of a city tyre, great for keeping out glass).
Personally I would go for the Schwalbe Big Apple. Nearly slicks so very fast (which offsets their relative weight) but still very strong and great puncture resistance. Plus(and this is the important bit) if you get them in the 2 inch version, you can use relatively little air pressure and have little rolling resistance. This gives you 'air suspension' (promoted by Schwalbe and bike brands on the continent such as Idworkx) and makes the on and off road riding a much more pleasant experience. I would always go with a fat (2" or more) tyre and in fact this is keeping me off the continental travelcontact (which is a skinny 1.9"). From experience I can say Swalbe Big Apples are pretty ok on dirt roads as well. I have one as rear tyre on my mtb (which I also use as tourer)in summer. If you feel more comfortable with continental, try the continental citycontact (don't be fooled by its name!), also an excellent tyre!
People are quite scared of using 'nearly slicks' on touring but it really makes a difference and can save you a couple of miles per day. Schwalbe realized this and now sells the Marathon Supreme, which would fit your tour very good as well, but is way overpriced.
edit: Marathon racers are ok for light trekking, but not really made to sustain heavy loads. For UK trekking they can be excellent though!