[tigor]

Does anyone recognise this as a part? Found it on the boot floor yesterday. Don't know if something has been picked up from the road or park and ended up in the car or whether this has fallen off some trim. Hesitant to throw away.

That's a reflection in the photo. It's not bashed.

[Peter_R]

That looks suspiciously like some kind of blanking cap with some kind of air pressure equalizing hole. You do not say what the size is, or whether it is plastic or metal?
I have just killed off an ants nest and the end of the powder canister there is a similar insert with the saw tooth serated edges for gripping it. One of a million suggestions I suspect. Keep hold of it just incase water gets in the boot.