Not even convinced that it is a seed capsule. Might it be an unformed flower bud that just got knocked off?? I would be tempted to gently take it apart...to see what lies inside.
The shape reminds me of the seed pods of grape hyacinths (muscari) but bigger and less papery-looking, so something from a bulb is possibly a good call.
Doncaster, South Yorkshire. Soil type: sandy, well-drained
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Might it be an unformed flower bud that just got knocked off??
I would be tempted to gently take it apart...to see what lies inside.