The UK (Westminster) Government has given a response to the petition on a petition calling on the UK Government to use the OpenDocument format for the storage of documents.
Read the UK Government’s response to the OpenDocument Petition

It seems that they are making no firm commitment to use the OpenDocument format, though are continually reviewing the format to store documents in, and converting them accordingly. They welcome the newer open standards, as it makes it easier to convert from one format to another.