Thanks for your patience.
I deleted and re-created everything making sure not to use the same name for the various aspects.
Good news is I was able to process a payment via Paypal.
Unfortunately, this has raised some additional questions.
1) Although I set the cart object to use British Sterling the Paypal system processed the test payment as $0.01 instead of £0.01. My PayPal account is configured for British Sterling as I am resident in the UK. I didn't see any other option for setting British Sterling except the one for the e-cart object.
I know PayPal send emails to the sender (customer) and recipient (business) detailing the transaction but when I configure a cart for my client this will use Sage Pay instead.
2) I have Universal Email 4 installed and activated but when I performed the Checkout step it skipped the email creation. I really need this to work so that both the shop owner and the customer get a copy of the order.
3) When the processing at Paypal completed there was no return to the checkout_success.php page. How is this done?