Further British interest in the area led to a brief attempt in the 1790s to establish a base on the island of Bolama, where there was no evidence of any continuous Portuguese presence. Between the retreat of the British settlers in 1793 and the official Portuguese occupation of the island in 1837, there were several attempts to establish a European presence on the island. Even after the Portuguese had asserted their claim in 1837, Afro-Portuguese lived and worked there alongside Afro-British from Sierra Leone, since Britain did not relinquish its claim to Bolama until 1870.