Its actually illegal to sell cigars and tobacco without a licence. As I found out on ebay trying to off load some 25 year old King Eddies and others..
That's an ebay policy because they can't ensure the buyer is over 18.
As far as I am aware, private sales of tobacco that has had duty paid to an over 18 is legal. Private means it must have been obtained for personal use and not have been obtained to sell.