Apparently not that easy to buy a decent TA curry in the UK anymore Robbo.
Nostalgia took me to my rather large pile of printed recipes from over the last decade. The pay for access website was called Real Curry Recipes and if you had your speakers turned up when you entered the site you were blasted with a heavy assault to the ears of some form of percussion / tympany type sound. They had an attached "shop" called the RCR Shop (web url now dead:
www.spices-of-asia.com).
While it is going to be hard to say anything new about "Base Gravy", I actually have printed out their version known as "The Body Base". It also contains information (formula) about their own "Mixed Powder" which must be made using their own "Supreme Curry Powder". If you use East End (or worse; Rajah) you will sacrifice flavour accordingly. If anybody is interested I can scan to pdf.
I seem to recall they also had a whole section concerning a method known as "The Melting Base" but I can't find anything relating to this.
The other thing I did find, dating back to 2013, is 2 pages printed out titled
The 'Original' Onion Base Gravy 3 Litre Version. There is a url provided which still works and takes you to a very little viewed Youtube video by JV. Only just over 1000 views in a decade. (Most BIR enthusiasts will know who JV is before clicking this link.)
https://www.youtube.com/watch?v=Hs6BEEhsVU4. The 2 pages I have printed out are numbered 54 and 55 so I assume it's from the eBook but I have no recollection of ever having it. Again, I can scan to pdf if anyone is interested.