The calendar (new style) act 1750 adopted the Gregorian calendar in England from 1752, and changed the start of the civil year from 25 March to 1 January.
So, 1748-03-24 (old style) would have been followed by 1749-03-25 (old style) in the Julian calendar.
And, 1752-12-31 (new style) would have been followed by 1753-01-01 (new style) in the Gregorian calendar.
There seems to have been some informal use of new style dates in England before this time. Pepys's diary used new style dates nearly a century before they were officially adopted.
Leap years in the period before 1752 occurred when the new style year was divisible by 4, even though the official calendar used old style years. This page provides evidence of this (in the discussion of the London Gazette), and this page notes the evidence from the Parliamentary Journal.
Does anyone know of an online calendar that presents a correct year-at-a-glance view of the official old style calendar with the correct leap years? For example, a calendar starting on 1595-03-25 and ending on 1595-03-24, and including 1595-02-29? None of the Julian calendars I have found online do this.
If nobody can come up with a web page I will have to write one, but that is quite a chore :-( especially actually getting it right.