It's identical to the bracket holding the white opaque bottle for the Trafalgar windscreen washer that came with my 1958 TR3A when I bought it brand new. Mine was not black on my TR3A but it was (and still is) plated in white zinc (silvery in colour). That bottle you see in my photo is 51 years old with the word "Trafalgr" in raised letters molded into the plastic around the bottle.
Tudor and Trafalgar were the two suppliers back then. Mine was "dealer installed" but the chromed nozzles on the "scuttle" had been factory installed.
BTW, my bottle you see there has been empty for the last 26 years, I emptied it in 1972 before I stuffed my "basket case TR3A" over in the corner of my garage and when I did the full restoration in 1990, I never filled it. I never needed it in the past 19 years during the 100,000 miles I have driven it. I don't drive on muddy roads, in the snowy slush and if it starts to rain - well who needs more water on the windscreen when it's raining ?