Thank you Henric, but that is what I had already tried. All such functions return nulls.
Interestingly, the document says to check if QlikView has interpreted the data as a number, and it hasn't. When I create a list box, the values are left justified, implying that they are strings. It doesn't say how to switch them back to being a number. The num(date) function fails.
Ex_date,date(date#(Ex_date),'DD/MM/YYYY') as Date1
This is my entry in the load script. Ex_date is the field name for the date values, Date1 is always null whichever date function(s) I use