A patent shall have to all intents the like effect as against His Majesty the King as it has against a subject:
Provided that any Government department may, by themselves, their agents, contractors, or others, at any time after the application, use the invention for the services of the Crown on such terms as may, either before or after the use thereof, be agreed on, with the approval of the Treasury, between the department and the patentee, or, in default of agreement, as may be settled by the Treasury after hearing all parties interested.