All company tax returns for accounting periods ending after 31 March 2010 delivered after 31 March 2011 will have to be filed online.
HMRC are to issue a leaflet to half a million companies and tax agents this month which outlines aspects of the changes. The leaflet specifies that all returns delivered after 31 March 2011 for accounting periods ending after 31 March 2010 must use a specified XBRL data standard for computations and accounts. The mailshot then goes on to say that the specified XBRL data standard is Inline XBRL (iXBRL).
Before April 2011, the CT600, accounts and computations may still be filed on paper, and accounts and computations, if required, in PDF format.