hey,

For Star Alliance (*A), you can find all the links at Star Alliance Useful reference.

Given that you are based in London, your best bet would be to start out in europe. In case of *A, It could be something like - Europe --> South America --> USofA/Canada --> New Zealand/Australia --> Thailand --> Europe.

On Europe --> South America you main choice is Lufthasa (LH), or TAP Portugal (TP).

On South America - USofA/Canada your choices are United (UA), Air Canada (AC), and US Airways (US).

On USA/Canada -- your choices are Air NewZealand (NZ), UA and AC.

On NZ/OZ to thailand - your choice is limited to Thai or via Singapore on SQ.

From Thailand back to Europe - u can do Thai Airways (TG), Lufthansa (LH), Scandinavian (SK) or Swiss Air (LX).

Other alliances could have their own rules/routing. But since I have only done RTWs on *A, can talk about those.

enjoy. cheers !!

PS: (of course you should go to Nepal from thailand ).