Metropolitan Railway takeover of Oxford & Aylesbury Tramroad services
By 1899 the MR and the O&AT were cooperating closely. Although the line had been upgraded in preparation for the Oxford extension and had been authorised as a railway in 1894, construction of the extension had yet to begin. On 27 November the MR arranged to lease the Tramway from the O&AT, for an annual fee of £600 (about £62,000 in 2018) with an option to buy the line outright.
 From 1 December 1899, the MR took over all operations on the Tramway. The O&AT's single passenger coach, a relic of Wotton Tramway days, was removed from its wheels and used as a
platelayer's hut at Brill. An elderly
Brown, Marshalls and Co passenger coach was transferred to the line to replace it, and a section of each platform was raised to accommodate the higher doors of this coach, using earth and old railway sleepers.
D class locomotives, introduced by the MR to improve services on the former Tramway line, damaged the track, and in 1910 the line between Quainton Road and Brill was relaid to MR standards using old track removed from the inner London MR route, still considered adequate for light use on a rural branch line. Following this track upgrading, the speed limit was increased to 25 miles per hour (40 km/h). The MR was unhappy with the performance and safety record of the D Class locomotives, and sold them to other railways between 1916 and 1922, replacing them with
A class locomotives.