After deleting an email address from Contacts is there any way of preventing it from popping up in the To: field of Mail when one starts to type in a contact name.

If when the address pops up it has a white arrow in a blue circle on the right, click the blue circle.

Toward the bottom, you will find an option to remove this address from the iPad's memory.

The ability to delete comes with iOS 6. Under iOS 5, you would need to restore your phone as new (which would, of course, update it to iOS 6).

if you are not on ios 6, then all you can do is wait. if you have deleted the address from your contact list, then it will live on for a while in your 'recently used' addresses. as you use new addresses, those older ones fall down the list, and eventually fall off altogether (unless you use them again). Have patience, it will go away.

Or do the update....