I am only now sure of this identification, because of this chunky roll of microfilm at Kew.
freebmd, and I had checked findmypast's death duty index to find that there was a will. I was now examining the indexes themselves on microfilm, part of the tortuous IR26 series. The first thing which leapt off the page was not the name Dickinson, which I was expecting, but that of Watson. The Watsons I quickly recalled where family of Mary's full sister Hannah, in fact it turns out Joseph was the eldest of that brood, and oldest male of the next generation. I needed to see his address - could that be Scale Houses, circled in orange? It surely was, and although the will disappoints by not stating him as nephew, in fact it would have been odd had she done so. It is enough that she chooses him as executor.