The proposed study is to examine the contribution made by John D'Oyly, a British Civil Servant, to the British acquisition and control of the whole of Ceylon. It is also aimed to examine the history of this period (between 1805-1818) in Ceylon as a part of British colonial expansion in South Asia focusing on the policy of infiltration which was used by the British as a method of expanding and consolidating their power and influence. In The Cambridge Illustrated History of the British Empire, published in 1996, P.J. Marshall submitted that the British had become a major political force on the south east coast of the Indian subcontinent, and had become the real rulers of the wealthy province of Bengal by the end of the eighteenth century. He further submits that the success of the British was mainly due to their ability to infiltrate into the internal politics of local states and kingdoms, and thereby dominate some of these political entities rather than overcome and destroy them by the use of military force. This process of infiltration will be examined in detail in the study of British relations with the Kandyan Kingdom, which was situated in the centre of Ceylon (Sri Lanka), and was the only local kingdom then in existence as an independent political entity. The primary documents to be studied are those that relate to the British relations with the Kandyan Kingdom between 1805 and 1818, which covers the career of John D'Oyly as a civil servant working in Ceylon. He was the principal figure used by the British in their dealings with the Kandyan Kingdom, due mainly to his proficiency in the Sinhalese language and his knowledge of the customs and manners of the local people. His official diary, covering between the periods of 1810 and 1815, is one of the major sources of this study, examining the methods of infiltration. What is attempted in this Thesis is to examine this new theoretical approach of infiltration (submitted by P.J. Marshall) to the history of British relations with the Kandyan Kingdom between the periods of 1805 to 1818. This study is associated therefore with giving a new dimension to D'Oyly's work as a civil servant, and also to give a deeper reason for British expansion in Ceylon (as much as in Asia) in the context of the broader British strategic objectives. It strives to give a new meaning to the primary documents available in studying British Kandyan relations, as a part of the successful political expansion of the British in India and Asia.