Adding php to header and footer

We use Newrelic to monitor our server. To best do this, I need to insert a block of php which generates javascript in the header and footer sent to the browser.

I found simple_structure_header.tpl and simple_structure_footer.tpl in the themes directory, but when I insert anything (php or html) in these files they don’t seem to get to the browser.

Can you advise how to do this?

Thanks Nigel

Files are : plugins/CoreHome/templates/header.tpl

Thanks. Sorted