The subreport is already in its own section and "suppress blank subreport" is already ticked.
The problem is that the subreport is not blank in that it returns one row. However, that one row is suppressed as a result of a formula that I have entered in the Suppress option of Section Expert so the actual number of rows shown on screen is zero.
The subreport is therefore not being suppressed because it thinks there is one record.
What I need is for the subreport to be suppressed if the number of rows shown is zero (after suppression has taken place).