Half a million people a day do it in the Telegraph. The Times claims almost as many, and the Guardian 300,000. Most people remember their first time, and everyone has a favourite. You can do it in bed, standing up, or on a train. You can do it alone, with a loved one or in groups. The Queen does it in the bath. It is not illegal, immoral or fattening. In fact it tops the Home Office list of approved entertainments for prison inmates. Crosswords are a very British obsession.