Hi Ashes,
The Kushi website does half answer the question as it has been asked by someone else.
The Kushi Chefs answer was this:-
"I recommend that for the recipes in this book you use pre-bought garam masala and curry powder.? Some restaurants make their own, and some don?t (I do both) ? but for the purposes of making dishes at home, it?s easier and more effective to use the bought variety.?
One word of warning though, we would advise against getting these from supermarkets, and would encourage you to buy them from traditional ethnic shops, where available.? They?re normally sold in small clear plastic bags (see Chapter Two of the book) and will be more like the varieties used in restaurants.? There are a number of different brands available, but we?d rather not recommend any one above another ? but as a general rule it?s considerably better to buy any one of these brands than it is to get it from a supermarket".
So there you have it, branded packets from ethnic shops are what they suggest we use as they claim they are "easier and more effective"
I am fairly sure a lot of BIR's buy branded spices in bulk as I regularly see what appears like restaurant owners in one large ethnic supermarket in Bradford with trolleys full of the biggest bags of spices you have ever seen and are commonly East End and Natco brands.
I am guessing they are restaurant owners just by the volume of stuff they seem to be buying.
Ray