Is this an honest question? Do you want an honest discussion about this issue?
At the time of the British Expeditionary Force, there was no colour bar to enlisting in an English regiment. Not to say that there wasn't a racist barrier to service but there were ME&B British soldiers as early as the Crimean War.
If you're seriously trying to play gotcha and suggest that my point is moot because of a selection of one illustrative screencap from an extended trailer then I can't fucking help you.
The onus is on you to find any representation of the IASC or an Anglo Indian BSM in the film. We know they were there. Why don't we see them?
British movies and media have a huge problem with representation, especially with Asian people. The only way it'll happen is kicking and screaming. There's a lot of Asian people in the country. The mayor of London is Asian. But, just like Black British, Asian British frequently go to America and become more famous.
At the end of the day this is a British movie by a British film maker. He lived in London. Edgar Wright lived in London. Lived in very diverse environments, yet all their movies are virtually exclusively white. Only Edgars hollywood movies seem to have a some tokens to appease American audiences who would not stand for the exclusively white nature of British movies.
The problem is British people don't care. Representation to them is the worst and most ugly side effect of 'PC Culture' breh. Even the BBC is insanely white.
EU recently created some diversity commision and put forth its plan for diversity in the EU. It only had policies for women. Not a single policy for black or other people of color. Representation for racial diversity just isn't a belief in Europe. It's scoffed at. Looked down upon.