Sultan said became increasingly concerned that British attempts to abolish the slave trade would weaken his power in the region. In 1842 he sent his envoy Ali Bin Nasur to London on the ship el-sultani to plead his case. Said's gifts for Queen Victoria included emeralds, cashmere shawls, pearl necklaces and ten Arab horses.

In reply, the British government told the Zanzibari ruler that it wished to abolish the slave trade to Arabia, Oman, Persia and the Red Sea. To soften the blow Queen Victoria gave Said a state coach and a silver-gilt tea service. (The state coach arrived in pieces and had to be assembled. It was still unused a year later, as Zanzibar had no roads. The tea service was considered too ornate to use and was taken to the British consulate for safe keeping.)

Britain continued putting restrictions on the slave trade. In October 1845 Said was virtually forced by Captain Hamerton to sign another anti-slavery treaty, which allowed slave transport only between lines of latitude 1° 57" S and 9° 20" S (between Lamu and Kilwa, the northern and southern limits of Said's dominions on the coast). This meant slaves could still be imported into Zanzibar but could no longer be exported to Oman.

Ships from the British navy were employed to help enforce the treaty by capturing any dhows carrying slaves. When a dhow was captured, it was set on fire and the slaves were taken to Aden, India, or a free-slave community on the mainland coast, such as English Point in Mombasa. However, with only four ships to patrol a huge area of sea, the British navy found it hard to enforce the treaty, so the slave dhows continued to sail. Ships from France, Germany, Spain, Portugal and America also continued to carry slaves, as there were still huge profits to be made. And on the mainland slave traders continued to push further into the interior.