Many thanks for your reply. I have added the Full Response and Full Request to the page and I acan see where the problem lies, although not sure where to fix it. It looks as if the the problem is with the CVV2, I have double checked the CVV code I am putting in for testing and it is correct.
The following is the Request and response I am getting on the failure page, I have replaced sensitive information with asterisks:
Your transaction could not be completed.
TRXTYPE=S&TENDER=C&BUTTONSOURCE=WebAssist_ASPVB_Cart_PRO2DP_UK&HOSTADDRESS=payflowpro.paypal.com&HOSTPORT=443&TIMEOUT=120&USER=*****&VENDOR=*****&PARTNER=PayPalUK&PWD=*****&ACCT=*****&EXPDATE=092011&TESTING=false&AMT=6.75&ORDERDESC=&L_DESC2=Ei EZ80&CURRENCY=GBP&FIRSTNAME=*****&LASTNAME=*****&EMAIL&STREET=*****&CITY=*****&STATE=*****&COUNTRY=GB&ZIP=*****&CVV2=***&FREIGHTAMT=3.75&HANDLINGAMT=0&TAXAMT=0&ITEMAMT=3&CLIENTIP=126.96.36.199&MERCHANT-SESSIONID=*****&L_DESC2=Ei EZ80&L_AMT2=1.5&L_QTY2=2&=
RESULT=114&PNREF=******=CVV2 Mismatch: 15004-This transaction cannot be processed. Please enter a valid Credit Card Verification Number.&AVSADDR=N&AVSZIP=N&CVV2MATCH=N&IAVS=N