Thank you again Tom - I no longer get the e mail when the transaction fails.
However _ I am sure there must be another issue - as there is nowhwere on the checkout where the customer has to enter their Card details !
I assumed this was to be done on the Sagepay Secure Server - so was expecting at some part to be transferred to their secure server to enter the card details. We never get to see this page.
Any more ideas ? Sorry to bother you again