Hi there... having real brain hurt with a stored procedure:

ALTER PROCEDURE [dbo].[SearchClaimants] 
	-- Add the parameters for the stored procedure here
	@criteria char(20),
	@col char(20)

	SELECT forename_str + ' ' + surname_str AS Name, nino_str as NINO, address1_str AS Address 
                FROM claimant 
                WHERE surname_str LIKE 'm' + '%'
				--WHERE surname_str LIKE '%ste%'
             ORDER BY Name

exec searchclaimants @criteria = 'm', @col = 'str_surname'

Now... this works and returns the expected results, but when I actually try to substitute the 'm' for the @criteria variable it doesn't work.
Can anyone tell me if there is a problem with using LIKE in a sp?