how about something like this:

set ANSI_NULLS ON

set QUOTED_IDENTIFIER ON

go

ALTER PROC [dbo].[bsp_intranet_product_search]

@ProductIdNVARCHAR(100),

@ProductDescription NVARCHAR(300)

AS

SELECT DISTINCT TOP 100 ProductId, ProductDescription, CrossReference,

ISNULL(CONVERT(VARCHAR,SUM(QuantityOutstanding)),'0') AS Quantity,

'£' + CONVERT (VARCHAR(12),StandardPrice,1) AS StandardPrice

FROM Products

LEFT OUTER JOIN dbo.Inventory ON dbo.Inventory.Product= dbo.Products.Product

WHERE (IsNull(RTrim(@ProductId), '') = '' OR [ProductId] LIKE '%' + RTrim(@ProductId) + '%')

AND (IsNull(RTrim(@ProductDescription), '') = '' OR [ProductDescription] LIKE '%' + RTrim(@ProductDescription) + '%')

GROUP BY Products.ProductId, Products.ProductDescription, Products.CrossReference, Products.StandardPrice