British Telecom (BT) is the world’s oldest telecommunications company. Its origins date back to the establishment of the first telecommunications companies in the United Kingdom. Among them was the first commercial telegraph service, the Electric Telegraph Company, introduced in 1846. As these companies amalgamated and were taken over or collapsed, the survivors were eventually transferred to state control under the Post Office. They later became a privatised company, British Telecommunications plc - the forerunner of today’s global communications company, BT Group plc, which serves customers in 170 countries.
See - https://www.btplc.com/Thegroup/BTsHistory/History_of_BT.pdf