Thank you for your reply but I know my OS (OSX 10.9), I was commenting that the solutions are only listed for MS products such as Word and not for Apple Pages and I have no MS software on my property.
The answer to the deficiency I have since discovered is a workaround that tricks the printer into believing that it is a media that isn't A4. So I selected a speciality media card and it was happy.
It would be more useful if the boffins at HP were to include a media called 'envelope' that would preclude the issue arising and the need for a workaround. Derrrr!