Brownsea Island by third parties, is owned by the National Trust. Most of the buildings are situated near the small landing stage. The northern portion of the island is a Nature Reserve managed by Dorset Wildlife Trust and an important habitat for birds; this part of the island has limited public access. A small portion to the southeast of the island, along with Brownsea Castle, is leased to the John Lewis Partnership for use as a holiday hotel for staff, and is not open to the public. The island forms part of the Studland civil parish in the Purbeck local government district.
Brownsea Island was sold to Kenneth Robert Balfour in 1891. Following the introduction of electric lighting, the castle was gutted by fire in 1896. It was subsequently rebuilt, and in 1901 Balfour put the island up for sale. The island was purchased by wealthy stockbroker Charles van Raalte who used the island as a residential holiday retreat. During this time the castle was renovated and served as host to famous visitors such as Guglielmo Marconi. Robert Baden-Powell, a close friend of the van Raaltes, hosted an experimental camp for boys on the island in the summer of 1907. Brownsea was largely self-supporting,