Sussed it!!
SELECT [Certificates Query].[Supplier Name], Sum(IIf([getcert]<0,1,0)) AS [Before Delivery], Sum(IIf([getcert]>=0,1,0)) AS [After Delivery], Sum(IIf([getcert] Is Null,1,0)) AS [Awaiting Certificate]
FROM [Certificates Query]
WHERE ([Certificates Query].[Arrival Date]) Between...