Weird ice balls in London?

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I received the following communication yesterday from Martin John Callanan, the (ahem) artist in residence at University College London's Environmental Institute:
Here is some important news I must share with you.

Late last night I began hearing reports of strange icy objects in a part of east London (UK) commonly referred to as Victoria Park. It was too dark to investigate and the park was locked until this morning. At dawn I set out to investigate, having only just returned to my office, this is the first email I write. What I discovered was so strange and unusual the first step was to upload the documentation to my website and contact you as a matter of urgency.

Within what appeared to be a rather contained area of roughly 200 acres coinciding remarkably with the boundary of Victoria Park, I found and recorded more than 300 occurrences of what I refer to as “ice balls”. These are roughly spherical objects ranging from ~30cm to more than ~150cm diameter. For now, until more information becomes available to me, I must surmise these “ice balls” are similar in origin to hail. Perhaps this exaggerated scale is the latest phenomenon associated to our rapidly changing climate.

I enclose a few images here, with the remaining 300 online at a special new website: