In short, I don't know! There is a core to it at the broken end, and it is a very unusual shape for a stone - hence my interest in it. I'll attach a couple of photos if I can, to give you a better idea...oh, I don't seem to have that option, now (?)...
Ah! Advanced editor! Here are some more photos. I do apologise - I have never tried to have anything identified before, and it may well just be a stone...
I am 90% sure it is just a stone; a piece of flint.
The other 10% allows for it being a burrow cast, as some flints are.
The white 'rind' is common in flints; the broken end exposes that and (in contrast) the darker core. Such rinds develop by weathering and/or chemical contact with the chalk/sediment in which they originated.
It is very common to find stones (especially flints) that 'look like something', but whose shape is really largely insignificant.
I think it's a piece of flint, on the beaches of the Holderness you find some fantastic shapes made from the same material coming from the Cretaceous chalk of the Flamborough cliffs and found as erratics on the Holderness coast.