I can see GOON but where does the Go on bit fit in?
I think the use of 'perhaps' twice suggests the John Major and John Sergeant answer is what the setter intends. It's a bit weak though unless there is a theme in this crossword
@fiction-factory Yes on reflection "GO ON" to mean "MAYBE" is not quite there.
I think @wzevon1951 is probably right that it's a reference to two famous Johns.
It was also our last answer to get.