On reflection I think it might well be the camera angle. Or rather, where the photographer is standing and the focal length used.
In the Press Association photo, Brian is to the left of the bottom edge of the far bench, almost in line with the middle of the far small crescent shaped patch of garden.
In my and bobm's photos the drain cover is almost in line with the nearer of the two crescent shaped patches of garden. The
PA▸ photographer was probably stood on or very near said drain cover.
Focal▸ length, photographer position and parallax differences between the PA, my and bobm photos have created the impression that the drain cover wasn't there during Brian's visit.
The next time I'm at Kemble I shall try to replicate the PA's photo and prove my theory.