I have just had some interesting chats with 2 Indian head chefs. I work as an IT recruitment consultant so I have access to thousands of CV's and luckily there were a few Indian chefs on there complete with mobile numbers and email addresses.
So first chef said he didn't think it was possible to perfectly replicate the BIR taste at home. This was mainly down to the large quantities they were making not working as well when scaled down to home cooking. He thought the base sauce (Curry King Vindaloo Base and Sauce recipe) sounded very good although he would usually use potato instead of carrot. He thought fresh base sauce was better than old stuff but they would usually use a batch for up to 48 hours.
The second chef was even more helpful and apparently runs cooking classes in Bristol twice a month -
www.myristica.co.uk. Although in his current job he is cooking posh indian food rather than BIR style, his previous experience was all BIR based.
He thought with the right ingredients and method it is perfectly possible to get the perfect curry at home, but it takes a lot of practice to get it right. He ran through the main 5 base sauces of traditional Indian cooking. The main one was our standard base in which he said they would use 10kg of onions and 3kg of fresh plum tomatoes along with the usual extras. He also said in India they only use red onions as the white or Spanish onions can taste too sweet. They also have a tomato based base sauce which is basically just tomatoes and onions, then there was a green base which was coriander based, a white base (cant remember what was in that one) and a very dry base. They would use scoops from each to make up the dishes. A Madras for example would 2 scoops of onion base and 1 scoop of tomato base (along with the other spices).
He confirmed that fresh base is better than old base so that myth is comprehensively dispelled now.
He was also nice enough to give me some onion bhaji tips which I'll get working on and post if they are better than my current version.
The final tip he gave was to add a sprinkle of chaat masala on the dishes before serving. This can be on everything from a CTM to a potion of Onion Bhajis. I've never tried the stuff before so I cant comment, but I'll be getting an order in soon.
I have an email address for both of them so I'm sure they would answer any specific questions anyone might have.