British diplomat who organized the Maritime Customs Bureau for the Chinese government in 1855.

In 1854 the Taiping Rebellion had cut off the Chinese trading city of Shanghai from the capital, Beijing, and, because the Western powers in Shanghai were required by treaty to pay a tariff on all goods that they brought into the country, they set up a bureau to collect the tariff for the Chinese government. Lay, as head of the bureau, made plans to extend its services to other Chinese cities and in 1861 was appointed inspector general of customs for all 14 ports through which Western goods entered China.

Two years later, at the request of the Chinese, Lay procured a fleet of eight gunboats with crews from the British, assuming the Chinese would transmit orders through him. They refused to allow such control to a foreigner, however, and the fleet was sold. Lay was discharged from his position as head of the Customs Bureau by the Qing government in November 1863 and was succeeded by the British diplomat Robert Hart.