The Grauniad changed to Berliner format in September 2005, and its sister Sunday paper The Observer made the same change in January 2006. Both changed to tabloids in January 2018.
The Observer is a national newspaper, even though it's a Sunday one. IMHO, despite the slight difference in dates, there is enough possibility of confusion for The Observer to have been allowable as an alternative answer.
© Macclesfield Quiz League 2018