I got an SMS messgae from my brother yesterday, telling me that Paya, not Nihari is the name of Bippin's special dish. It certainly doesn't mean that last weekend's visit to the Lahore Karahi was wasted though, as I've picked up the Nihari spice mix and I will certainly be brewing one up in the slow cooker overnight some weekend soon.
It turns out that Paya means trotters. I have found a great article on the dish here, which says "Mughlai cuisine has quite a few preparations of Paya but the ones most popular are the Nihari, the Shorba and the Salan", so we may not have been that far off the mark.
One of the reviews that the Lahore Karahi has posted in its window as an advertisement says - I kid you not - that one of their specialities is "something disgusting made with sheep's feet". I bet that's Paya, and I feel another visit coming on.
(It is worth noting that another advantage of regular visits to the Lahore Karahi is that it does give you a rather more positive image of Moslem youth than the hate crazed smack dealer in cartridge belts that the red tops have been feeding us.)