It is now compulsory for limited companies to send their Company Tax Returns online using iXBRL for accounts and computations. The new requirements are effective for returns delivered on or after 2011. It will no longer be acceptable for most companies to send either the accounts or computations on paper or as a PDF attachment to an online return. The new requirements are effective for returns delivered on or after 1 April 2011, for any accounting periods ending after 31 March 2010.