OK I understand now that it could be difficult to get the kind of tool I'm thinking about but the SQL option isn't really a good workaround as it wouldn't cut down on the time spent creating and testing reports for customers.  Thanks for making it clearer to me though.

But as far as I can see and understand, it doesn't "step through" in the way that you imagine. I constructs a single SQL query based on the elements that you have defined in the report and then fetches the data which is then populated back into the report variables.

What I was thinking about was being able to have the normal Design view but also an extra 'Code-watch' view within Report Designer that shows the report stepping through the code during runtime.  This would be much more helpful and useful than using SQL statements to view report data.

Hi Chris, I've looked at the SQL code option you suggest but this isn't what I was thinking of and would take just as long as amending and test running the reports in Report Designer I think.

Looking through the code for the Report Designer, I think that that is a big ask - it is a very complex engine. They may be able to to add some trace instructions to give you feedback at strategic points. Bad table links etc., would be very evident from the SQL code that is executed unless it is using transient data. I find that the best way to design reports is to construct them or parts of the report in SQL first - would this not help with avoiding bad table links etc?