UK communications law could be used to spy on physical mail

An anonymous reader writes: The BBC reports that the UK's Draft Communications Bill includes a provision which could be used to force the Royal Mail and other mail carriers to retain data on all physical mail passing through their networks. The law could be used to force carriers to maintain a database of any data written on the outside of an envelope or package which could be accessed by government bodies at will.
Such data could include sender, recipient and type of mail (and, consequentially, the entire contents of a postcard). It would provide a physical analog of the recently proposed internet surveillance laws.
The Home Office claims that it has no current plans to enforce the law.