CT600 E-Filing Guide

Click the links below to jump to a particular section:

Step 1 - Register as an agent

Step 2 – Entering the Practice ID and Password

Step 3 – Generating the Electronic Return

Step 4 - Transmitting the Returns



Step 1 - Register as an agent

Practices may register for Online Services at www.hmrc.gov.uk. Your Agent Reference should be available from your local tax office.



Step 2 – Entering the Practice ID and Password

  1. Log into Business Tax as the Master user.

  2. Select Setup, Practice Options and click Tax Options.

  3. Select the Corp.Tax tab and enter the practices User ID and Password.  

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Step 3 – Generating the Electronic Return

Users may now generate electronic CT600 returns by selecting Reports, Electronic Tax Return.

Multiple Corporation Tax Accounting Periods

Where an accounting period consists of more than one CTAP a return for each CTAP may be required.  Select the relevant Corporation Tax Accounting Period from the drop down list to generate the return for that CTAP.

The first CT600 submitted should have the accounts and computations attached. On any subsequent CT600 covering part of that same period of account the field on page 1 ‘if no accounts say why not’ should be completed with: ‘See CT600 for the period DD/MM/YYYY’.

Live / Test

Select ‘Live’ or ‘Test’ in the Electronic return status section. Where test is selected this will be indicated on the Transmit Internet Return screen.

New / Amended

The default return status is set to New. To submit an amended return set the radio button to ‘Amended’ in the New / amended return indicator section.

Attaching Accounts

Accounts must be attached unless the user has indicated otherwise and given a reason on the Data Entry - Summary screen.  

Use one of the following radio options to locate the accounts:

Attach Computation

iXBRL or PDF computations should be attached to the CT600 unless the user has indicated otherwise and given a reason on the Data Entry - Summary screen. There are four options available:

Additional Attachments

Users may attach additional PDF documents to the return.  

  1. Select External PDF to locate an existing PDF for the client or Communication Tracking to attach PDF's which have previously been saved within Communication Tracking.

  2. Click OK to generate the report(s). Once the report(s) have been generated and reviewed a message will be displayed informing the user that the internet submission has been stored.

  3. Click OK.

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Step 4 - Transmitting the Returns

  1. Select Reports, Transmit Internet Return and highlight the return(s) to be submitted.

  2. Click Transmit and wait for the return to process.

  3. When this is complete Cancel will change to Close.  

  4. Clicking Close will display a message for each return transmitted which will either:

For more information regarding error messages log on to the knowledge base at http://practice.iris.co.uk/customer_support/support_tools/knowledge_base.aspx to search for the relevant error number. Note that error 3001 is confirming that an error has occurred; the error number quoted after that is the one which indicates the nature of the problem.


Practice Management users may add an extra level of security to the Transmit screen to prevent transmission of returns before they have been approved by the client.

To switch on the functionality the practice must update the tax return job profiles for individuals, partnerships, limited companies and trusts as follows:

  1. Open System Maintenance

  2. Select Practice followed by Job Types / Profiles and for each of the tax return jobs:

    1. Click Profiles.

    2. Highlight the job stage that indicates a tax return has been approved by the client and select Edit.

    3. From the Automatically complete when drop-down list select the Approval Received from Client event and click OK.

    4. Click Save and then Close the profile.

Once this has been set users will not be able to transmit electronic returns unless the approval job stage for the client has been completed. Unapproved returns will be listed on the Transmit Internet Return screen in grey with ‘No’ in the Approved column and the Transmit button will be disabled.

Once approval has been obtained the job stage may be completed either from the job itself or by clicking Approved on the Transmit Internet Return screen.


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