Many people will be aware of the launch of "OS OpenData" in April 2010. However, this does not mean that all the Ordnance Survey data is now available free of charge.
Only selected datasets were released at that time. The most popular map series for print publication (the 1:25,000 scale maps) were not included, nor were postcode sector boundaries. The result is therefore a compromise - not quite all that The Guardian had campaigned for (in its "Free Our Data" campaign).