The British didn't create the caste system from scratch, but they had a huge role in shaping what became the modern caste system. I'm sleepy, so I'm going to quote direct from this BBC article (though it's a good amount article, if you have the time. It does a good job for a summary, imo)

"[Britain's reshaping of Indian society] was done initially in the early 19th Century by elevating selected and convenient Brahman-Sanskrit texts like the Manusmriti to canonical status"

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" [The caste] categories were institutionalised in the mid to late 19th Century through the census. These were acts of convenience and simplification."

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"The colonisers established the acceptable list of indigenous religions in India - Hinduism, Sikhism, Jainism - and their boundaries and laws through "reading" what they claimed were India's definitive texts."

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"There is little doubt that the religion categories in India could have been defined very differently by reinterpreting those same or other texts."

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"In fact, it is doubtful that caste had much significance or virulence in society before the British made it India's defining social feature."

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"The colonisers invented or constructed Indian social identities using categories of convenience during a period that covered roughly the 19th Century.

"This was done to serve the British Indian government's own interests - primarily to create a single society with a common law that could be easily governed."

"A very large, complex and regionally diverse system of faiths and social identities was simplified to a degree that probably has no parallel in world history, entirely new categories and hierarchies were created, incompatible or mismatched parts were stuffed together, new boundaries were created, and flexible boundaries hardened."

"The resulting categorical system became rigid during the next century and quarter, as the made-up categories came to be associated with real rights. Religion-based electorates in British India and caste-based reservations in independent India made amorphous categories concrete. There came to be real and material consequences of belonging to one category (like Jain or Scheduled Caste) instead of another."

Apologies for just quoting at length at you. I fear that presenting info this way will give the sense that I am lecturing you, but that is not my intention; a large part of why I share this info is because I learned of this relatively recently and I was astounded by how significant Britain's role was.