There's a new book out, Duel in the Snows: The True Story of the Younghusband Mission to Lhasa, by Allen, Charles about the 1904 British invasion of Tibet.
From the summary on the Free Tibet website, the invasion seems to have been a typical British imperial operation, motivated partly by geo-political rivalry with Russia, partly by the greed and adventurism of the officers involved, and started on the pretext of 'a trivial border incident involving some Nepalese yak-herders [which was] declared by [Lord] Curzon [Viceroy of India] to be [an] 'overt act of hostility' on the part of the Tibetans'. It involved the usual crimes, including a battle that turned into a massacre at Chumik Shenko, looting of religious artifacts (now in the British Museum, naturally), violence and death-threats to prisoners, and negotiations in bad faith, designed to break down so that further military advances could be made with reinforcements called up.
Colonel Francis Younghusband, leader of the British forces, put into the peace treaty an article 'requiring the Tibetans to pay an indemnity of half a million pounds over 75 years, during which time the Chumbi Valley was to be occupied by Britain, and a 'separate agreement' giving the British Trade Agent to be based at Gyantse the right to visit Lhasa for consultations. These two clauses were inserted by Younghusband in defiance of orders, and concealed from his Government until the Treaty had been signed. They were immediately repudiated and Younghusband was ordered to stay on and renegotiate the treaty, which order he ignored.'
Naturally Younghusband got a hero's welcome when he got back to England: 'lauded by the British press, received in private audience by the King, greeted with rapturous applause when he lectured at the Royal Geographical Society in London and at the Scottish Royal Geographical Society in Edinburgh. He received honorary doctorates from the Universities of Edinburgh, Bristol and Cambridge.'
The expedition's local expert, Dr. Waddell, was equally culpable, carrying out the looting, beating and death-threats mentioned earlier, perhaps unsurprisingly given his low opinion of Tibetan culture: he wrote a book arguing that Tibetan Buddhism was a perverted form of the religion.