Yes it's outside the Pavilion, but to me the proliferation of medals suggests that they were post 1914-1918 army rather than police. I have a copy of a similar photo showing another band outside the Pavilion, but the publication I found it in (dated 1894) stated that the band was made up of men from the local reserve.

Police Bands do exhist and the fact that several of the bandsman are wearing Pith Helmets tends to bear this out, however to my knowledge Brighton has never had a Police Band, if I am wrong then please don't hesitate to inform me. To my knowledge most of the Police Bands tend to be in the Midlands or the North of England,hope this is of some use to you.