The FT is reporting that the hacked contractor, SSCL, holds the payroll details of most of the British armed forces and 550,000 public servants, including central government.
The key line: "It was set up in 2013 [under a Conservative government] as a joint venture between the cabinet office and Paris-based Sopra Steria, a digital services company, as part of a wider drive by the government to reform the civil service and save taxpayer money by centralising functions."
https://www.ft.com/content/b21c9eba-54c4-46c6-bd99-e9554c4660d9