DAVID FROST says:
So do I and it worries me! There’s nothing to stop you leaving shotgun cartridges or blank ammunition in your car but although it’s lawful it’s not sensible.
The rules governing the storage of rifle ammunition are more strict and are the same as for the rifle itself.
You are committing an offence if you leave rifle ammunition lying around where an unauthorised person can get hold of it.
It should be locked away at the time you lock the rifle up. Leaving it on the parcel shelf is illegal.