HMRC published guidance for companies who had to submit their company tax return form (CT 600) before 1 June 2008 for a period that ends after 31 March 2008. That return included calculations based on the new rates announced in the Chancellor's Budget in March 2008. Companies affected by these rate changes were advised not to use Corporation Tax Online services before 1 June 2008.

If a company needed to deliver a return before then for a period that ends after 31 March 2008 and that return included calculations based on the new rates it can still deliver a paper return direct to its HMRC office.

The changes to the rates of corporation tax on profits affect the tax calculations of most companies as the main and small companies' rates and marginal small companies' relief fraction used from 1 April 2008 have all changed.

Click http://www.hmrc.gov.uk/ct/new-services.htm to access the guidance.