In addition to his professional activities as a botanist, in the 1930s Kingdon-Ward also served as a spy for the British India Office. In 1935, Kingdon-Ward was arrested by Tibetans after he crossed the Sela pass into the Tawang tract ( now Tawang District of Arunachal Pradesh, India) despite being refused permission to do so by the Tibetan authorities who were then administering Tawang. Tibetans protested this violation of their border to the British mission then visiting Lhasa. Kingdon-Ward was quickly released, but this incident led the British to investigate the status of the border, and it was discovered that the entire Tawang tract had been ceded to British India by Tibet by the Simla Convention negotiated by Sir Henry McMahon with the Tibetans in 1914.