Myself and 4 other travellers from the UK will be visiting Lhasa from Kathmandu in August/September 2013. We are booking an overland tour to Lhasa and then intend to travel onward via train to Xian. I'm aware that there is a direct service and that if it is booked in China it is far cheaper than booking through an online company here in the UK. However, we will only arrive in Lhasa 2/3 days before wanting to take the train to Xian and so I wondered if tickets are likely to be sold out by this point? We are in Nepal from early August until leaving for China in very late August/early September. Wonderful place though I believe Lhasa to be, we'd rather not get stuck there! Can anyone advise me on what might be the best course of action?