I think the whole BIR business has changed beyond recognition over the last 20 odd years. In the 60's and 70's most BIR's were independent small family enterprises, the owners were in many cases also the chefs and took great pride in what they did, their reputation and therefore livelihood depended on providing good food and looking after their customers.
During the 80's and since we have seen the growth of the BIIR (British Industry of Indian Restaurants) with its own trade magazine(s), bodies, restaurant chains (national and local) and the proliferation of pre-prepared ingredients, take a look at the Booker trade catalogue sometime.
The days of the individual chef/proprietor are long gone and sadly I fear the knowledge base that was so cleverly and carefully built by them is fast disappearing also. These days it seems we have restaurants run by bean counters who through market research dictate that what the customer wants is fast service, good food and they want it cheap. As anyone who has worked in any service industry can tell you, only two of those conditions can be met at once, so invariably the quality of the food suffers.
More people are eating out than ever (recession, what recession?) but what are they eating? The Korma and the CTM now dominate and make no bones about this, any chef will tell you the easiest way to disguise poor/cheap ingredients is to smother them in fat and/or sugar so this suits the restaurant owners and the non-discriminating customer down to the ground. What suffers of course is the trickier, more difficult to 'fake' dishes, like bhuna, madras, etc. as the whole industry moves ever further 'downmarket' in attempting to pander to the lowest-common-denominator with ever blander more stanardised fare in the pursuit of greater profit.
If you still have an old style artisan chef/owner run BIR or T/A local then count your blessings and give them your custom, they are a dying breed unfortunately.
Rant over, regards
CoR