I think I have solved it! Whilst viewing 'distorted' channel I changed to 4:3 mode. This 'sqaured' the viewing area but righted the picture. Changed back to 16:9 on another channel and now pictures auto-formats depending on which cannel I am on! I can't find any reference to this in the TV manual and am assuming it is Scart Control in the Sky Box menu conrolling things. For some reason it seems to have needed 'triggering' somehow, as it were.
Thank you very much for taking time to assist.