I obviously know where to put that code - I asked a stupid question.
This morning, clear mind [from problems - see below].
I had by mistake deleted the header.php from catalog/controller/common !
Therefore created me some ‘other’ problems with a Hackers defence which I slowly fixed + the fact I did not have a Piwik API in header.php.
Foa ny other with similar problem, put the code within the header - it seems to work perfectly now.
I know of others using it in the footer.php [it should be fine too]
It had taken 14 days [of hell] with my ADSL host to have them call out BT to fix line, which they did within 2 days!
They do not believe a experience Electronics and IT Technician with 35 years experience in Telecommunications - plonkers!