The UK Government has mandated the use of Open document formats by all government bodies. The
selected standards are PDF/A and HTML for viewing government documents and Open Document Format (ODF) for sharing documents. ODF is the native format used by the free open source LibreOffice/OpenOffice software package. The Office Open XML format, as used by Microsoft Office, is not one of the formats chosen for use by the UK Government. The Australian Government is unclear as to its preferred files formats. The most advanced agency in use of ODF is National Archives of Australia, who adopted the format for long term storage of government documentsTheir Xena open-source software converts documents from Microsoft formats to ODF.
A quick search showed 83 ODT documents at Gov.au, 265 at Gov.uk and 1450 at Gov (US).