The data isn't secret, but commercial access to the database is restricted. If you want to find a few postcodes (I think <=5 per day) it's free. More, or if you want a manipulatable copy of the dataset you need to pay.
The only thing it does is keep postcode methods of geo-location unavailable to the UK public. Canada, Australia, the US and most of Europe are already moving forward here because they don't have this restriction... the UK loses out.
This isn't capitalism, nor is it socialism. It's a kind of corporatism in which the risk―the money spent speculatively mapping Britain, arguing in Parliament, drawing up postal code boundaries―is entirely assumed by the public, but the reward―access and profit-taking―are entirely given to the private sector.
Same goes for the Ordnance Survey. Luckily, they’re in the process of being taken apart online by OpenStreetMap. Having said that, their paper maps are wonderful.
it is not true that the "reward [is] entirely given to the private sector." the royal mail is owned by the government, so the profits extracted from selling the postcode database could be viewed as subsidising other services. (post in rural areas, for example)
