Some interesting replies here...
I've experimented for many years with various cooking options and have settled on my current favourite set up of a Bushbuddy with Tatonka SS alcohol back up, nesting inside a 1ltr SS Tatonka billy which in turn nests inside a 1.6 ltr SS Tatonka billy - leaving enough room inside for brew kit, spice bottles, and maybe a boil in the bag meal or some noodles/ couscous etc. This covers all bases for me - I can bake, steam, boil and fry; I have multifuel options - including an open fire where allowed and I just prefer SS cookware - I can taste the aluminium in water boiled in it and titanium creates too many hotspots for my liking. Also, titanium and aluminium are not as easy to clean, in my experience, as SS. Like I said - I've arrived at this set up after many years of (expensive!) experimentation and would not stray from it...unless I was embarking on an adventure such as you describe - then I would have to think again.
The problem with this set up for your purposes is weight and the fact that you'll be carting it around on your back for a year or two. I would suggest that for a trip like this - on foot - you have to think about weight very carefully and literally count the ounces. A lot of the commercial, lightweight options out there are really only good for boiling water and I would suggest that meals based on this (rice, noodles, cous-cous, boil in the bags etc) are going to pall after a couple of weeks! At some point you are really going to want to cook - as opposed to just boil water.
My choice for a trip like this (and for no other reason) would be a Trangia UL HA (Ultralight Hard Anodised) - in 25 or 27. The anodisation would alleviate some of the taste/ cleaning issues, it's a lightweight complete cooking system and, for the UK leg of the trip at least, you're never going to be too far from fuel. Depending on your drinking preferences - I'd take along an insulated mug as well - although my personal favourite is a kuksa (black coffee and brandy being two of my drugs of choice!) - and don't forget the utensils as well (see how the ounces are adding up!). You should already have a knife so a lightweight spork should do the job.