I've sent single jars of honey to friends in Berlin via Royal mail. I filled in a little customs sticker, which is placed on the outside of the parcel. They often taken longer than expected to reach their destination, but I've only had one jar returned, that was due to me making a mistake in the address.
I used to run online businesses. Often when receiving a customer order for a destination outside of the EU, it was recommended we use Royal mail, as parcels were then far more likely to get through customs.