This simple, functional and attractive building I believe is an electricity substation in New Street, Brighton. It is surrounded by a carpark which makes it rather stand out. The question that arises to me, was it purpose built?
From memory, there are only the two doors that are visible and none other. The very tall one seems to be an odd shape for moving electrical equipment through. I would date it about 1920, which probably is about the time electricity was being spread around the land.
No evidence of any wires going to it or where they might have connected before power was put underground. What are the strange almost ground level openings? Ventilation? They appear to be boarded up.