Thanks Mark, and everyone else. I think we can say conclusively that this is Boulters Lock. A similar view was taken during the enlargement of the lock (see below; this photo is dated April 1912) you can see exactly the same bush on the right, but without the hotel sign, and the building is identical (compare the stone string course at first floor level, and open windows). And it's still clearly visible in Loddon's streetview picture above. The date of the the Getty images photo also means that my grandfather's picture must have been taken before the enlargement, perhaps some time 1910-1911.
So, case closed, and thanks to you all.
Best wishes,
David