In olden times, finding a coin in a Christmas pudding was apparently a sign of good luck, but now it is more of a liability concern.
Diners at the High Timber restaurant in central London who ordered the traditional Christmas pudding on Christmas Day got a Christmas waiver form that they were asked to sign before eating the pudding. Neleen Strauss, the restaurant's owner, said the waiver had been suggested by some of her customers, many of whom are lawyers. "I thought it was going to be a pain," she said, "but decided to do it to cover my backside."
It does seem a bit odd to deliberately hide a foreign object in something you know people are going to eat, but since this tradition has apparently been around for about five hundred years, by now maybe anybody eating a Christmas pudding should be considered to have assumed the risk of wolfing down a lucky (or unlucky) coin.