Never been to War and Peace so can't appreciate the scale of the event, but plenty of sites up North I can think of as suitable for a large event.
Manby show ground near Louth, Lincolnshire used to host the wheels event years ago and steam rallies still had plenty of room for expansion.
Flookburgh airfield near Cark, Cumbria. I was there for the second year running and this large airfield was no-where near full for a large mixed event so should cope with several hundred MV's no problem.
Plenty of hard standing at both sites as they're ex airfields. A reasonable off roading area at Manby too.