I have found a pretty ugly work around but I post it here because I cannot find any solution to this on the internet and hope this could help someone else.
I hope someone can provide a better solution but if you change the .csv file so that the line:
,01/02, 02/03, 03/04, 04/05
Is changed to:
," "01/02, " "02/03, " "03/04, " "04/05
It will force a space before the numbers and stop Excel formatting the cell. Now, of course, this is a rather invalid way of fixing this but it is better than having my row reformatted entirely out of context.
HTH (and please post better workarounds)
David