To flesh it out a little, here's the query I'm using at the moment..
SELECT [GWPI-Combined].[Agency Number], [Commissioned Expenditure Data].[G/L Account No], Sum([Commissioned Expenditure Data].Amount) AS SumOfAmount, GSC_CRR.[CRR Value], [GWPI-Combined].[GWPI 2012], [GWPI-Combined]![GWPI...