Adding weekday name to x-axis in a chart

I am trying to add a weekday name to the horizontal axis in a chart (SSRS).

In horizontal Axis Properties I went to number, then Custom, and added:

=(WeekdayName(Fields!Date.Value))

It nearly works. I have put in this week's dates into the parameters (23/02/2015 - 28/02/2015) but the x-axis is showing the dates as numbers, eg 23 - 24 - 25. I'd love to see the words Monday, Tuesday et al in there instead.

When setting up the chart I have Fields!Date.Value as the category group, at the moment grouped on =day(Fields!Date.Value)

Any suggestions on how to get 'Monday', 'Tuesday' etc to appear would be much appreciated.

I have tried

=weekdayname(weekday(Fields!Date.Value)). This partly works but 
unfortunately repeats the day of the week the report was run, eg Monday Monday Monday rather than Monday Tuesday Wednesday et al.

Thanks.