Changing back button in iOS 7 disables swipe to navigate back

IMPORTANT:
This is a hack. I would recommend taking a look at this answer.

Calling the following line after assigning the leftBarButtonItem worked for me:

self.navigationController.interactivePopGestureRecognizer.delegate = self;

Edit:
This does not work if called in init methods. It should be called in viewDidLoad or similar methods.