If your local branch has the self service machines all you have to do is click "no" when the screen asks if your parcel contains a prohibited item. Which saves time, and suggests Rapidnick is, strictly, right in his approach to counter staff

However personally I haven't got time or energy to argue with staff with a little authority who think that things they don't approve of should be banned (see also, idiots who think Swiss Army knives are illegal cough Bristol post office cough). So now I would use the machine