The OS is not the only government department to charge for data originally collected at taxpayers' expense, but it is probably the most notorious. What is more they all charge each other and local councils - also part of government! There is an argument that the OS's costs are reduced by selling its data but this is well outweighed by experience in other countries. Where data is made available freely, it spawns lots of entrepreneurial businesses, which add to a country's infrastructure, growth and economy generally.
The Guardian has taken up the cudgels against the government on this issue, as it has on Freedom of Information. To follow the ongoing discussion, look at the Technology section of The Guardian each Thursday.