Well I bit the bullet and did a factory rest. I also did not link the 'phone to my, little used, Google account after the reset.
It works fine with NO ADVERTS!
The downside was that the dreadful KIES software (Samsung's ghastly offering) didn't back up any downloaded apps which is no big deal.
It also solved another problem which had appeared after several months of use and that was that every address book entry downloaded twice to my car system whenever I got in the car resulting in the car's 'phone memory being full before all my contacts had been copied. It was something to do 'Connections' where a contact was shown with more than one 'Connection' whatever that means!
I consider myself fairly tech savvy but so much of the stuff that seems to be part of the Android system strike me as utter crap.
Thanks for all the suggestions.