Agent Credentials vs Company Director: Filing CT600 for Multiple Companies

When you submit a CT600 through TinyTax, you choose how to authenticate with HMRC at the submission step — using either the company's own Government Gateway credentials, or an HMRC-authorised agent's credentials. This choice is made per-filing and is completely independent of which TinyTax plan you are on.

Two Filing Modes

Company Director

Use this when the person submitting is a director or officer of the company who has access to the company's own Government Gateway account.

• Enter the company's 12-digit Gateway User ID and password
• Corporation Tax must be enrolled on that Gateway account
• Most common for owner-managed companies filing their own returns

Tax Agent

Use this when you are an HMRC-authorised agent (accountant or bookkeeper) with Corporation Tax authorisation for the client.

• Enter your own agent Gateway User ID and password
• Your client does not need their own Government Gateway login for Corporation Tax
• HMRC agent authorisation must be in place before submitting

Does Portfolio Require Agent Credentials?

No. The Portfolio plan simply allows you to manage multiple companies on a single dashboard — it does not require or restrict which filing mode you use.

With Portfolio you can:

• Submit some companies using their own company director credentials
• Submit others using agent credentials
• Mix freely on a per-company basis

The plan determines how many companies you can add to your dashboard. The submission credential choice is made independently at the time of each filing.

Common Questions

I am filing on behalf of a client — which mode should I use?

If you have your client's Government Gateway login, choose Company Director and enter their credentials. You do not need formal HMRC agent registration for this approach.

If you are a registered HMRC agent with Corporation Tax authorisation for the client, choose Tax Agent and enter your own agent Gateway credentials.

Can I use different modes for different companies on the same Portfolio plan?

Yes. Each filing is independent. You choose the mode at the submission step for each company individually.

Does using agent credentials affect the filing in any way?

No. Both modes result in the same CT600 being submitted to HMRC. The only difference is whose Government Gateway account authenticates the submission.

I have a group of companies — do I need separate Gateway accounts for each one?

Yes. HMRC's Government Gateway is set up per company. Each company in a group has its own separate Government Gateway Organisation account, with its own 12-digit User ID and password.

When you file CT600 via TinyTax, you enter each company's own credentials at the submission step — you will use one set of credentials for the parent company and a completely separate set for the subsidiary. There is no way to "add" a subsidiary to the parent company's Gateway account; they are two distinct HMRC online accounts.

To file for the subsidiary you need:

1. A separate Government Gateway Organisation account for the subsidiary (its own 12-digit User ID and password)
2. Corporation Tax enrolled on that account
3. The subsidiary's UTR (10-digit Unique Taxpayer Reference — HMRC sends this in a letter shortly after incorporation)

If the subsidiary has filed online before (via HMRC's own software or an accountant), a Gateway account already exists — you just need the 12-digit User ID and password for that account.

If CT has never been filed online for the subsidiary, you'll need to create a new Organisation account. Log in at gov.uk/log-in-register-hmrc-online-services, choose "Create sign in details", select "Organisation", then add Corporation Tax as a service. HMRC will post an activation code to the subsidiary's registered address (usually 7–10 working days).