Problem with Dates only accepted in American format

Hi all,
I've created a report that rejects dates input in any format other than American, being a british organisation this is obviously an issue.
"The value provided for the report parameter 'StartDate' is not valid for it's type".
The report calls a sproc (which is definitely not to blame), I've checked the properties of the report, they are set to UK English.
Any ideas, people?
Thanks - and a happy Easter weekend to all!!

Jaybee.