You've heard about it on T.V , radio, and just about every major chat show. British retail companies spend over 300 million pounds each year to supply prizes for competitions, just to get customers attention on their products.   

These competitions take several different forms,  the most common is the Compvert.
This is where you read an advert, and answer a question about the product or service. This is a very cost effective way for a company to advertise,  and the bigger  the prizes on offer, the more people read them !

In any given month there are literally thousands of competitions being run. People all around the country try the occasional competition,  "name and address on a postcard" and send it "With their answer".  then forget about it. After all its a One in a million chance of winning !