Abdul Mhd and the guy who runs the Kushi Balti House, Mhd Ali Haydor, are two very kind and generous exceptions to this situation. They've worked in BIRs for decades and, presumably, really know their stuff.
But, increasingly, the so-called experts who are now writing most of the books which claim finally/absolutely to reveal secrets of the special BIR tastes are Brits who, until recently didn't claim to know any more than the rest of us.
Is this the fault of the Kindle revolution, whereby any Tom, Dick or Harry can self-publish a book? At least in the old days, a book publisher might demand some evidence that the author had credible experience and qualifications, and a non-fiction book had been properly checked and tested.