I should be away doing the Lhasa/Kathmandu Red Spokes trip that Kojaklollipop did right now, but the trip was cancelled a few weeks ago as its impossible for UK passport holders to get Tibet visas at the moment . . . . Chinese government took offence at the recent visit to the UK by the Dalai Lama and their retaliation is to withhold visas. Situation will probably change by the time you do your trip, but I’d suggest that you make sure that you can get full refunds on any flight tickets that you might book – just in case. Red Spokes were brilliant at refunding their element of the trip cost.
I’ve done four Red Spokes tours in the past (Tajikistan, Bolivia/Peru, Laos and NW Vietnam) and as Kojaklollipop said the experience is vulnerable to the dynamics of the group – so far I’ve been lucky and have always had a fantastic time.