Date imported from another workbook, change display format

I am pulling in a date from another workbook via ='[am3.xlsx]am3-Peu used (VS)'!$F$1

It is coming over as 30/09/09 which is how it is formatted on the other workbook.

I want to display it as Sept 09.

I have tried playing with the cell formatting (in the cell with the formula) but it stays the same 30/09/09.

Any ideas?

Regards BVG