File a Company Tax Return – Find HMRC's online filing software
Go to the 'Welcome to Online services' page at www.online.hmrc.gov.uk
On this page, go to 'Existing users' on the left hand side and type in your User ID and password. Then click the ‘Login’ button.
You'll be taken to the 'Your HMRC services' page where you need to follow the 'Access service' link.