My sincere thanks as ever, Graham!

This is a much better way of entering a date and as you say, helps to eliminate potential errors in date entry by the user.

Alas, it would appear that although the date on the UserForm indicates a UK format of DD/MM/YYYY, when the "Update Document" button is pressed, it shows the date in US format of MM/DD/YYYY. If you run the UserForm again without changing the date, it then updates the document with the UK locale. In fact, each time you press the "Update Document" without changing the date, it flips between UK and US formats and swapping the day / month.