The London themed decor tree at John Lewis Oxford Street. If I had space for two Christmas trees in my house, I'd make one London themed. Each year I see lots of lovely London/Britain themed decorations (especially in Harrods, Liberty & Selfridges) but find they probably won't fit in with my Christmas tree!
The Trafalgar Square tree; y'know the tallest tree ever!
Another tree I loved at Polhil was this newborn/baby themed tree - the blush & baby blue surprisingly works!
The last tree I am especially envious of and that is top of my to see list before the 4th January is the Disney Tree at St Pancras station in London - a tree made up of Disney toys, yes please!