Let it be now that henceforth the Celestial Emperor has decreed that all imports of opium into the Great Qing Empire banned.
Any citizen of the Empire found guilty of trafficking opium will be executed on the spot.
Any foreigners discovered importing opium or trafficking opium will lose their rights to a factory in the canton.
Trade will be conducted via payments of silver, as the Great Qing Empire does not need any other goods

Thus the Emperor has decreed

EDIT:
The emperor has appointed scholar-official Lin Zexu to the position of Special Imperial Commissioner. Lin Zexu will be tasked with eradicating all opium trade.
As his first act, he has written a letter addressed to Queen Victoria of Great Britain.
Read it here
TL;DR
Opium trade is illegal in China, Her Majesty is hereby informed of this fact and thus can no longer claim ignorance on the matter. We hereby inform her that we intend to fully eradicate the opium trade in China, and we urge Her Majesty to cooperate on this matter