Hi All, I've been asked to look at speeding up the following SP - my TSql is very limited. I ran Show Execution Plan and it indicated that the query's on the LetterHistory table accounted for 68% of Query cost - I have no idea as to how I can achieve the results any other way - here is the query in all it's glory

ALTER PROCEDURE [dbo].[GetClaimDetailsByMasterRefDev](@MasterRef char(10)) with recompile
AS
set dateformat dmy
Declare @POALetterCode int
Declare @PIFLetterCode int
Select @PIFLetterCode = dbo.GetLetterCode('PIF',@MasterRef) -- 20
Select @POALetterCode = dbo.GetLetterCode('POA',@MasterRef) -- 21
SELECT	
dbo.Claim.ClaimRef,
dbo.Claim.MasterRef,
ClaimStatusDesc = CASE dbo.Claim.ClaimStatus
	When '01' Then 'Inc' 
	When '02' Then 'Chk'
	When '03' Then 'Agr'
	When '04' Then 'Rej'
	When '05' Then 'Adm'
	Else '' end,
dbo.Claim.ClaimStatus,
dbo.Claim.CreditorName,
dbo.Claim.ClaimNarrative,
dbo.Claim.PayDetailsID,
dbo.Claim.AdmittedValUSD,
convert(varchar(10),dbo.ListNos.listdate,5) As AdmittedDate,
dbo.PaymentDetails.PayAddressID,
dbo.PaymentDetails.PIFStatusCode,
(CASE WHEN ((dbo.Claim.PayDetailsConf = 0)
	OR  
	EXISTS (Select PayDetailsID From TTDetails Where PayDetailsID = Claim.PayDetailsID
	And TTDetailsConf = 0)) And ClaimStatus = '05' THEN 'Y'
	WHEN ClaimStatus != '05' THEN ''
	ELSE 'N' END)
As PIF,
dbo.Master.CorrAddressID,
convert(varchar(10),dbo.Claim.PayDetailsConfDate,5) As PayDetailsConfDate,
dbo.Claim.PayDetailsConfUser,
dbo.Claim.PayDetailsConf,
PayDetailsRequestedDate = (Select convert(varchar(10),Max(LetterSentDate),5)
From dbo.LetterHistory Where claimref = claim.claimref and lettercode = @PIFLetterCode),
PayDetailsRequestedUser = (select top 1 LetterSentUser from letterhistory
where LetterSentDate = (select max(LetterSentDate) from LetterHistory 
Where LetterCode = @PIFLetterCode And ClaimRef = Claim.ClaimRef) And ClaimRef = Claim.ClaimRef),
(Select Distinct convert(varchar(10),Max(DateReceived),5)
From dbo.PayDetailsReplies
Where ClaimRef = Claim.ClaimRef) As PayDetailsReceiveddate,
 (Select Top 1 InputBy 
 from PayDetailsReplies
 where 
 DateReceived = (select max(DateReceived) 
 from PayDetailsReplies 
 Where ClaimRef = Claim.ClaimRef)) As PayDetailsReceivedUser,
dbo.Address.CountryCode,
dbo.Listnos.luxoruk,
dbo.Claim.AdmittedListNo,
dbo.multiblk.block As PayBlockCode,
PayBlockDescription = 
multiblk.block + ': - ' + rtrim(blockpay.blkd_desc) + ' - '
+ multiblk.raised_by + ' - ' 
+ convert(varchar(10),multiblk.raised_dt,5),
(select count(block)
from dbo.multiblk
Where active = 1
and clm_ref = dbo.Claim.ClaimRef) As NumBlocks,
(CASE WHEN EXISTS
(SELECT block
FROM dbo.multiblk
WHERE dbo.multiblk.block = '40' 
AND 
dbo.Multiblk.clm_ref = dbo.Claim.ClaimRef 
AND 
dbo.Multiblk.Active = 1) 
THEN 'Y' ELSE 'N' END) 
AS GadFlag,
(CASE WHEN EXISTS
(SELECT block
FROM dbo.multiblk
WHERE dbo.multiblk.block = '94' 
AND 
dbo.Multiblk.clm_ref = dbo.Claim.ClaimRef 
AND 
dbo.Multiblk.Active = 1) 
THEN 'Y' ELSE 'N' END) 
AS Deceased,
Art39.BenstatusCode As DBO,
(Select distinct(convert(varchar(10),Max(LetterSentDate),5)) 
from LetterHistory
Where LetterCode =@POALetterCode
And ClaimRef = Claim.ClaimRef) As POADetailsRequestedDate,
(select distinct(LetterSentUser)
from letterhistory
where 
LetterSentDate = (select distinct(Max(LetterSentDate))
from LetterHistory 
Where LetterCode = @POALetterCode)
And ClaimRef = Claim.ClaimRef) As POADetailsRequestedUser,
(Select convert(varchar(10),Max(DateReceived),5)  
from POADetailsReceived
Where ClaimRef = Claim.ClaimRef) As POADetailsReceivedDate,
(select distinct(InputBy) 
from POADetailsReceived
where 
DateReceived = (select Max(DateReceived) 
from POADetailsReceived 
Where ClaimRef = Claim.ClaimRef)) As POADetailsReceivedUser,
DBOReceivedDate = (Select convert(varchar(10),Max(DBOReceivedDate),5) From dbo.DBOSReceived
Where dbo.DBOSReceived.ClaimRef = Claim.ClaimRef),
DBOReceivedUser = (Select DBOReceivedUser From dbo.DBOSReceived
Where dbo.DBOSReceived.ClaimRef = Claim.ClaimRef And DBOReceivedDate
= (Select Max(DBOReceivedDate) From dbo.DBOSReceived
Where dbo.DBOSReceived.ClaimRef = Claim.ClaimRef)),
lds.due,
lds.dpbflag,
lds.adjustflag,
lds.empdivflag
From dbo.Claim 
Left Outer Join 
	Listnos
	ON Claim.AdmittedListNo = Listnos.AdmitList
Left Outer Join 
	Art39
	ON Claim.ClaimRef = Art39.ClaimRef
Inner JOIN
	dbo.Master 
	On  dbo.Master.MasterRef = dbo.Claim.MasterRef
Inner Join 
	dbo.Address
	On Master.CorrAddressID = dbo.Address.AddressID
Inner Join dbo.PaymentDetails
	On PaymentDetails.PayDetailsID = dbo.Claim.PayDetailsID
left outer join 
	lds.dbo.vw_cms_claims_main lds
	on dbo.Claim.ClaimRef = lds.claim_reference
left outer join multiblk
on Claim.ClaimRef = multiblk.clm_ref And multiblk.Status = 1 And multiblk.Active = 1
left outer join blockpay
On blockpay.blkd_code = multiblk.block 
Where dbo.Claim.MasterRef = @MasterRef
Order By Claim.ClaimRef