The new version of the Company Tax Return form (form CT600 version 3) must be used for accounting periods that start on or after 1 April 2015.
In addition, a new computation taxonomy has been introduced for computations that accompany the new CT600 form.
The old version of the CT600 form (version 2) and computation taxonomy must still be used for accounting periods that start before 1 April 2015, including accounting periods that span 1 April 2015.
Commercial software developers are aware of these changes and are updating their online filing products. HMRC’s free downloadable filing software has also been updated. Please ensure that you are using software capable of producing the new version of the CT600 form and XBRL tagged computation for accounting periods that start on or after 1 April 2015.
Source: gov.co.uk