Ok I solved my problem of pop up Games Centre during games by disabling the multiplayer access in restrictions in General settings, so thanks for the signpost sci fan supermoderator - a mouse with a hat icon personage
Actually, rewind! It's come back. I have no idea how to get rid of it, it only started in the last week or two. May simply buy a book of Sudoku and stop playing online! A bit defeatist perhaps.... But I'm bored with it now.