Thanks for the reply - i've changed the Cell format within excel to display dates as dd MONTH yyyy - so in this case, they're correct. HOWEVER, the actual system date, or the date that was passed to excel was 09/03/2020 or 10/03/2020 which in day MONTH year format should be 9 March 2020 or 10 March 2020, and is instead 3 September 2020 or 3 October 2020.
I think i have found where my error was. Using formatdatetime(utcNow(), 'dd/MM/yyyy') and passing the resulting output to Excel will give me the wrong date format in Excel. After changing how I format the date in the function, i have an acceptable solution:
FormatDateTime(utcNow(), 'yyyy/MM/dd')
I am now going through all my flows to check all the filters i have to make sure the correct date is being passed back to Excel and vice-versa!