First English Slave Voyage: It was in 1562 by Sir John Hawkins

First English Slave Voyage: It was in 1562 by Sir John Hawkins, which was an encroachment on Portugal’s monopoly of Africa.  Slave trade dropped as British foreign policy in 1783, thus indicating 221 years of the trade.  The trade was sharply stimulated by the establishment of the British colonies in the Caribbean and the introduction of the sugar industry.”
Companies Involved: Company of Royal Adventurers (which held a monopoly), which was replaced by the Royal African Company in 1672 (after the war with the Dutch).  Note the ties to the royal family.  “The policy of monopoly…provoked determined resistance…” from merchants and planters, the latter “…demanding free trade in blacks as vociferously and with as much gusto as one hundred and fifty years later they opposed free trade in sugar”.  The monopoly was complete: purchase and control of ships, sale of Negroes, importation of plantation produce.  Opposition to other monopolies was also common: 
“In 1698 the Royal African Company lost its monopoly and the right of a free trade in slaves was recognized as a fundamental and natural right of Englishmen”. The Royal African Company, once losing its competitive advantage, received parliamentary subsidy, only to abandon the slave trade in 1731, when it abandoned slaving in favor of traffic in ivory and gold dust. Gradually its powers lessened and it became unable to maintain the complex network of …"…lands, forts, castles, slaves, military stores, and all other effects…". “In 1750 a new organization was established, called the Company of Merchants Trading to Africa”. For many years His Majesty’s Exchequer had defrayed all the Company’s expenses via Parliament, and it was finally decided to, in effect, transfer the Company to public ownership, incorporating the lands in the colony of Sierra Leone.   "The Act for Extending and Improving the Trade to Africa"