The phrase Selling coal to Newcastle is an Australian colloquial saying that is used for several different situations. This follows other Australian language customs of utilising words that may be inappropriate for some people, but are bloody brilliant for others. It also demonstrates another Australian custom of using a single phrase to refer to as many things as possible so they can be as lazy as possible. The phrase stems from Newcastle, a town on the New South Wales coast that used to produce coal and dole bludgers, an Australian term for a type of welfare bludger. Nowadays in only produces dole bludgers.
Selling coal to Newcastle can be used in a variety of situations. In most cases it is used to indicate that the suggested action is foolish, futile, fruitless, or dumb. This references the fact that attempting to sell a surplus item to a supplier of that item is unlikely to be successful. The phrase is usally used as "That makes about as much sense as selling coal to Newcastle". Other related phrases that people with a larger vocabularly are likely to use are "If you believe that then I've got some waterfront property in the Sahara desert for you to invest in" and "What are you drunk?".
Alternatively the phrase can be used to mean the opposite. In this case it is a compliment to the person themselves if they are particularly skilled at debating, marketing, or haggling. Thus the phrase becomes "he could sell coal to Newcastle". This is similar to phases such as "he could sell paintings to the blind", or the American favourite "he could sell refridgerators to the eskimoes". People usually use this to refer to con-men.
A final use of the phrase occurs in school aged children. To say one is "Selling coal to Newcastle" means that they are doing study. While truthfully mean that they are not doing study. Parents don't understand though, which makes it cool.
In recent years the primary export of Newcastle has been steel, as pure coal production halted in the 1960s. In 1911 BHP offered to build a pollution production plant in Newcastle that could double as a steel mill. After steel production overtook coal production there were suggestions that the saying should be changed to "Selling smog to Newcastle" since it sounded much catchier. However in order to be politically correct the mayor of Newcastle changed the saying to "Selling steel to Newcastle", as steel was now nominally the third highest export behind pollution and dole bludgers.
edit Steel Mill Closure
BHP announced the closure of the steel mill in 1999. Large protests were held at the mine as the closure would have meant that the phrase would have to be changed once again, this time to "Selling dole bludgers to New Castle", which did not roll off the tongue as easily as the other sayings. Thousands of people demonstrated to protest against forcing the name to be changed once again. A national referendum was held shortly after the closure of the mine to decide if Australia was to become a republic. Several ringleaders of the protests snuck in an extra line on the ballot. Thus it was changed from asking if you support Australia become a republic or remaining a constitutional monarchy, to asking if you support becoming a republic and changing the saying "Selling steel to Newcastle" into "Selling dole bludgers to New Castle". Or if you support remaining a constitutional monarchy and changing the saying back to "Selling coal to New Castle". Needless to say more people wanted to remain a constitutional monarchy than accept the messed up "Republic" that they were suggesting.
edit Recent Examples
A chinese firm, Zhongguo Kilts. Inc, recently began mass producing kilts and has been shipping them to Scotland. Due to a stroke of luck, when the first shipment arrived the local kilt-weavers were all striking to get better working conditions. The chinese firm were able to come in with their cheap imports and steal all the business away from the local manufacturers.