From 1 April 2011, all Company Tax Returns for accounting period ending after 31 March 2010 must be filed online with accompanying accounts and computations in Inline eXtensible Business Reporting Language (iXBRL) format. In preparation for this, HMRC updated their CT Online service on 23 November 2009.

The main features of the online service will be the same, however many existing filing software products that enable taxpayers to file their Company Tax Return online will not be accepted by HMRC systems since 23 November.

The current CT online return form was withdrawn and replaced with updated software on 23 November 2009.

Data cannot be accessed through the CT online filing service after 19 November 2009.