Originally Posted by grimslade
According to manton, a jacket with hacking pockets should be center-vented, if I understand him correctly.
I won't presume to speak for Manton, but I don't believe this to be the case. A hacking jacket has both hacking pockets and a center vent, traditionally, as the vent allows the jacket to spread nicely over one's horse. But hacking pockets have become common on sportcoats and more casual suit jackets, removing them from their equestrian context. To me, at least, there is no reason that they must be accompanied by a single vent.