I can remember Chili Powder (as you said), and also Curry powder (Vencat, light blue = mild, Pink = Hot) being available in the 60s/70s but not a lot of anything else, maybe some other members can think of some more, and put them on this thread, and we may well come up with some answers.
Maybe they just used the curry powders :
OK, in reverse order : no, they (the Indian restaurants, that is) definitely used more than just curry powder : I know this because on my very first visit to an Indian restaurant ("The Maharajah of Chislehurst", owned by a Mr Chowdhury : I remember his name because it was the same name as the owner of an Indian restaurant I used to frequent in Nottingham during the period 1970 -- 1973.) Anyhow, I was taken aback by the sheer intensity of the heat, and said to the waiter "Even the rice tastes hot : do you use curry powder in it ?". "No sir", he said, "not curry powder : other spices". This would have taken place during the period 1963 -- 1970, and earlier rather than later : maybe 1965/66.
As to curry powders, yes, I remember "Vencat"s (I think that was a foreshortening of the real name -- something like "Vencatachellum", perhaps ?) but I used to buy my spices from a central London Indian grocer (and, later, from similar grocers in the Birmingham/Smethwick/Walsall area), and there the spices were in bulk. Of course I have no idea how many spices he sold, but of curry powders alone there was a considerable choice, that I do remember, and even more varieties of dal.
And some evidence (not as substantial as I would like) that there was almost certainly more than just "curry powder and ground chillies" right from the outset :
"As the influence of the British in India grew, so did the interest in Indian food back in Britain, leading to the publishing of recipes and the commercial creation of curry powder in 1780."
Sp, pre-1780, there were presumably spices but not curry powder.
"In 1935 Veeraswamy's was sold to Sir William Steward, M.P., who ran the restaurant for 40 years. He travelled the world in order to source produce and was dubbed 'the curry king' by The Times."
He would hardly have "travelled the world" just to buy curry powder !
"If you had visited Veerawamy's, as it was then called, in December 1959 you could have enjoyed Chicken Tandoori (allow 15-20 minutes) for the princely sum of ten shillings and sixpence. "
Perhaps you /could/ make tandoori chicken using just curry powder, but I suspect they did not.
All quotations from
http://www.menumagazine.co.uk/book/restauranthistory.html. It would be well worth researching Sir William Steward, M.P., further : he may well have left written evidence of the spices he brought back to England.
E P Veerasawmy (1963) lists the following as being available : cinnamon, cumin, allspice, cardamom, turmeric, coriander, ... (this just from the text up to page 22).
Mrs Beeton (1860) lists coriander seed, turmeric, cinnamon seed, mustard, ground ginger, allspice and fenugreek
seed.
Hannah Glass (1747) lists peppercorns, coriander seed, white pepper, cloves, and mace.
The last two are just from the most casual inspection : I am certain more spices would come to light from a thorough reading.
So, I think we are fooling ourselves if we believe that the ingredients available to BIR chefs in the 1960s were significantly less varied than today; of the spices that we now use as a matter of course (turmeric, chilli, coriander, fenugreek, paprika, cumin) I would bet a very substantial sum that all were easily available and widely used at that time.
** Phil.