I want to know the answer to the following question:
What law did the British make to cause the use of the Gregorian calendar?
All the background I'm provided with is that "They can indicate that the start of the Julian year has been adjusted to start on 1 January (NS) even though contemporary documents use a different start of year (OS); or to indicate that a date conforms to the Julian calendar (OS), formerly in use in many countries, rather than the Gregorian calendar (NS).". Is that enough to answer the question?
Answer: no