I live just down the road from this and also fairly near Runnymede and can visit and take pics if people want. As to RAF Northolt, there are still flights there. The road goes past the airfield and there are runway lights by the road. Sometimes you have to wait while a plane arrives.
I happened to drive past the Polish Memorial today at around 3pm. There was a very well attended ceremony going on at the time, several hundred people with large Polish flags. Does anyone know why that would be?
There was a ceremony at Lommel today as well. Plechtigheid op Poolse militaire begraafplaats They've just identified the grave of a Polish Lancaster crew member, Mikolaj Kirkilewicz by DNA analysis. Unfortunately, I can only find references in Polish or Dutch ! Lommels graf krijgt na 74 jaar een naam dankzij DNA-onderzoek Lost on a raid on Cologne with 300 Squadron on 2nd March 1945 . His name is currently on the memorial at Northolt. I'm not sure if it is co-incidence that he was lost on 2nd March as the Belgian reports seem to imply that it is a regular ceremony.
See The discovery of the remains of Lieutenant Nicholas Kirkilewicz, pilot of the 300 Bomber Squadron Mark
What a shame this can't be done with unknown BEF graves in France and Belgium. The Belgian authorities are apparently prepared to allow it.