>And the other way round: For sure, Opium was imported to England. Why didn't it become a problem?
Opium was produced around Calcutta(Kolkata). Shipping it to China was cheap, shipping it to the UK was expensive. Only the wealthy British could afford opium, and they used a ton of it. See https://en.wikipedia.org/wiki/Confessions_of_an_English_Opiu...