Thanks, but just noticed something else.
If in the admin screen I change the payment method to Pay On Delivery when the customer goes into the 'My Orders' screen the button shows as 'Pay with Collectionondelivery' - payment method shown as all one word.
Looks like the text is coming from the plug-ins element name (element column of extensions table).
As its in the order listing template I can change the code for this, but it would be better if the default behavour displayed something like 'Pay with "Collection on Delivery"'.
Where Collection on Delivery comes from the name field on the payment method configuration page.