The most difficult part of the project was the construction of the Beacon Hill Tunnel, which ended up costing about one quarter of the whole project. Together with the construction of the Sha Tau Kok line, a two-foot narrow gauge branch railway from Fanling to Sha Tau Kok (making use of the rails and rolling stock used in the construction of the main line and later closed in April 1928), the final cost was HK$12,296,929, making it one of the most expensive railways in the world and, as costs escalated, the subject of much concern in both Hong Kong and London.