In October 1914 the Jullundur Brigade was one of the first brigades from the Indian Army to go into action on the Western Front. ...
Sikh historian Peter Singh Bance said Sikhs and other Indians fought with the British Army corps, such as the 1st Manchesters and the 47th Sikhs fighting as one.
I haven't seen the film - is it set entirely in 1917?
The 1st Manchesters and the 47th Sikhs (Jullundur Brigade) appear to have left the Western Front by 1915/16 - two Indian cavalry divisions remained - is the actor rising a horse in the film?
"Three battalions from different parts of the world, with different cultures and different beliefs were placed together.These were the 1st Manchester's, the 47th Sikhs, and the 59th Scinde Rifles.Together they became known as The Jullundur Brigade."
1st Battalion
29.08.1914 Mobilised for war and sailed for Europe from Karachi, landing at Marseilles on 26.09.1914...
10.12.1915 Received orders to move to Mesopotamia and embarked at Marseilles for Basra and arriving 08.01.1916. this was to reinforce the British army fighting the Ottoman Empire in that area and assist in the liberation of Baghdad.
"The average Indian battalion had 764 men when it landed; by early November the 47th Sikhs had only 385 men fit for duty."..."The two Indian infantry divisions were withdrawn from France in December 1915, and sent to Mesopotamia"...
"Two Indian cavalry divisions remained on the Western Front until March 1918"...
discovery.nationalarchives.gov.uk/details/r/2f8ff186-2a81-47b1-a949-5f01c9a9ab9a
www.forces-war-records.co.uk/units/275/manchester-
regiment
"Of the 1.4 million Indians recruited for the First World War, some 563,369 were non-combatants, or “followers”, though their particular kind of war-work is rarely mentioned in the literature."
Not glamorous enough for the film probably;
"In February 1917, the government of India undertook to provide 50,000 labourers for France as well"
encyclopedia.1914-1918-online.net/article/labour_india