This white telephone kiosk is one of only three in the country. The Lord of the Manor paid the Post Office to paint it white in the 1920's. As such, in 2005 it became a Grade II listed building.
A great picture, but just a couple of points. This style of telephone kiosk, the K6, was not designed until 1935, and presumably installed shortly afterwards. A local resident, Sir Thomas Dundas, arranged for the kiosk to be painted white in the 1940s. He was a director of Barclays Bank, but not Lord of the Manor. There are several white, or, arguably, cream, kiosks in Kingston-upon-Hull as the town had its own non-BT telephone service. Ignoring those, I always understood there were a few more white kiosks than three, but certainly the Slaugham one is not "unique".