In general, it is useful to see inside such flints. In this case, I don't see anything particularly useful, however.
So, it may be be a flint that is spherical by chance (they do come in all shapes and sizes).
But it could also be a fossil sponge, like the one IDd and very well explained by Luanne on this forum a couple of years ago
BTW, such flints can have archaeological significance, too
Many thanks for your feedback and the links which I've checked out. I'm left puzzled, I'm pretty sure it isn't a fossil sponge, it seems to be a solid ball of grey / brown flint, there is no evidence of the sponge texture. Having searched a bit, all the photos I've found show a relatively thick white coating, usually with a textured / pock marked / orange peel surface whereas this is relatively smooth without much covering. When I first saw it I thought it was an old tennis ball that had lost all its fluff. I've attached a couple more photos fyi.
Thanks for the further photos.
The last one shows a couple of little arcs, suggestive of part of a gastropod (snail) fossil.
Flints can show a range of rinds. They are usually in the white-grey-orange-brown spectrum. They may be orange-peely or smooth. Smoothness can arise from polishing (perhaps of an orange-peely rind) by wave action on a beach (we know yours comes from a beach). In the beach/wave environment, as well as being ground around, stones are tossed against one another, which is probably the explanation for the fractures in your specimen. Given enough time, the fresh (darker grey) surfaces will turn whitish due to exposure to the atmosphere and weathering. If you look at broken flints in old walls, you'll see many surfaces which once were a fresh dark grey, but which now may be slightly milky.
Lack of a spongey texture does not mean your specimen was not derived from a sponge. Many fossils are casts. That is, the original animal's hard parts dissolved, leaving a cavity; the cavity then became filled with other material mimicking the shape of the original but entailing none of its internal structure.
In the cases of most fossil casts, the shape clearly shows the fossil origin. But with spherical casts, eg. from Porpsphaera sponges, the overall shape is ambiguous - because flints can form in random shapes including spheres.
More on flints here
And a couple of refs re banded flint, which you may come across, and which is often mistakenly guessed to have a fossil origin: