The fruits of Euonymus europaeus, the spindle tree or, more accurately, spindle bush. I come across several of these distinctive bushes on my walks, both round Whiteknights Park and Chazey Wood, but it was only last week that I took the trouble to identify them. I had assumed that they were a foreign species that had escaped from gardens but they are actually native to Britain.
This is what the leaves look like:
Photos taken in Whiteknights Park, Reading, UK, on 2012-10-14.