Fernando Po is a strategically important island off the coast of West Africa. It's ideal position had made the island highly sought after by various European navies including the Dutch, Portugese, Spanish and also the British. Unfortunately, it's ideal strategic position was still very much in the highly diseased equatorial zone that had earnt West Africa the nickname of 'White Man's Grave'. Therefore many of the settlement attempts ended in failure. In fact the Spanish abandoned the colony in 1827.
The vacant strategic location of the island came to the attention of the Royal Navy who were engaged very actively in an anti-slave trading campaign. West Africa was the obvious source of many slave bound for the Americas. The Slave trade in the British Empire was abolished in 1807 and in fact slavery itself would be abolished throughout the Empire in 1832. The Royal Navy had its work cut out for itself in policing this policy along the West African coast. There were a myriad of river deltas and coves for slavers to hide or to gather their human cargoes. Fernando Po would be the ideal base for Royal Navy patrols to resupply and interdict slavers from.
The British used the port on the North coast as their main base of operations. It was renamed Port Clarence in honour of the Duke of Clarence who became William IV. The base was never a popular destination for British sailors as disease was still a major problem. However the population of the island did increase substantially due mainly to numbers of freed slaves. This was often the first port of call for Royal Navy ships after they had confiscated slaves from illegal slavers. Many, but not all, of the slaves remained on the island and set up a new life for themselves.
The success in reviving the colony meant that the Spanish were keen to have a second look at their colony. From 1844, they stated their intention to resume control of the islands but it would take another decade before they formally did so. One other factor in the return of the Spanish was the success of protestant missionaries in gaining converts on the island. Needless to say, Catholic Spain felt that their own missionaries should be doing the converting and lobbied hard for the British lease to be revoked. This was done in 1855.