Plaque

Wikipedia says "Every May, supporters of the Szmul Zygielbojm Memorial Committee gather at the memorial."

The New Yorker gives the address of Zygielbojm's flat as 12 Porchester Square, which, from the current street numbers, we believe was on the site  redeveloped in the mid-1970s into the yellow-tiled block of flats, The Colonnades, at the south-west corner of the square.  The New Yorker also explains that, in 1991, the plaque could not be erected on Zygielbojm's home because a resident of one of the 5 flats there, a Jewish survivor of the Holocaust, was afraid that, were the plaque erected, the building would become a target for anti-Semites. However, if we are right about the location of no 12, then that building did not exist in 1991, and its replacement, The Colonnades, had more than 5 flats.

The article also talks about "the garden behind the apartment" so we think it likely that the address of Zygielbojm's flat was actually 12 Gloucester Terrace. These houses back onto the gardens of Porchester Square so the error is understandable.