The CT603 is a form we send out to companies regarding them needing to file a return based on the records we hold.
The CT600 is the form we need submitted following the notification of CT603.
The CT600 however must be filed electronically, we do not accept paper copies of it unless its an amendment to the original which was filed electronically.
You can see the CT600 on the HMRC Website.
Depending on your circumstances you may be able to use our free filing service if you look at :
Check if you can use the HMRC Corporation Tax online filing service
It will point you in the right direction, or there are filing only agents that will submit the return or if you have an accountant they may be able to submit it for you.
There is lots of information on Corporation Tax