Thanks for your reply.
This is the method that I am using at the moment and it does work to the extent that the displayed page header can show the image on page 1 and the text on other pages.
My issue is that if the letterhead image is tall (say 4cm), the page header has to be set at 4cm high to display the image.
When the image is hidden on subsequent pages and the text box is displayed (which is say 1cm high), there is 3cm of white space between the bottom of the text box and the first line of body text.
Is there a way that the page header height can be set dynamically might be a better question? If there is, will having different page header heights on different pages affect rendering to say PDF or Word?