Filing CT600B – Controlled Foreign Companies (CFC) Supplementary Pages

The CT600B is the supplementary section of the UK Corporation Tax Return used to report interests in Controlled Foreign Companies (CFCs), claim relevant exemptions, and disclose certain hybrid mismatch arrangements.

If your company holds a 25% or greater relevant interest in a foreign company controlled from the UK during the accounting period, you may be required to complete the CT600B — unless the entity qualifies for an exemption such as the Excluded Countries Regulations, the Tax Exemption, or the Low Profit Margin Exemption.

This article explains when you need to complete the CT600B, the information required, and how to approach key sections.

If you would like to read more about Controlled Foreign Companies (CFCs), do not miss our comprehensive guide.

1. When to Complete the CT600B

You must complete the CT600B if:

• Your company held a 25% or greater relevant interest in a CFC at any time during the accounting period; and
• The CFC’s accounting period ended within or at the same time as your company’s accounting period.

You should also complete it if:

• The company is a hybrid entity;
• The company has transactions with hybrid entities in the same control group;
• There is a deduction/non-inclusion mismatch or a permanent establishment (PE) mismatch;
• A counteraction has been made under Part 6A of the Taxation (International and Other Provisions) Act 2010 (TIOPA 2010).

You do not need to include a CFC on the CT600B if:

• The CFC meets one of the statutory exemptions (Tax Exemption, Excluded Territories, Low Profit Margin, or Exempt Period Exemption); or
• The CFC is not, in fact, a CFC, but would pass an exemption test if it were.

This exemption avoids unnecessary compliance costs where it’s clear the UK company would not have a CFC charge.

2. Information Required in the CT600B

You’ll need:

• Company details (name, Unique Taxpayer Reference);
• Period covered (start and end dates, maximum 12 months);
• Details of each relevant CFC:
  • Name and territory of residence;
  • Type of exemption claimed (if any);
  • Percentage of apportionable profits;
  • Chargeable profits;
  • CFC tax charge;
  • Creditable tax already paid;
  • Reliefs (e.g., under Chapter 9 loan relationships);
  • Any restricted Advance Corporation Tax (ACT).

Where a CFC charge applies, the total is reported in box 490 of the CT600.

3. Foreign Permanent Establishment (PE) Exemption

If you have made an election for the foreign PE exemption, you must indicate if this is the first period it applies. This exemption can prevent profits attributable to a foreign PE from being taxed in the UK, subject to specific conditions.

4. Hybrid and Other Mismatch Disclosures

From April 2022, additional disclosure boxes (B40–B85) require completion if the company:

• Is a hybrid entity;
• Has hybrid entity transactions within its control group;
• Has deduction/non-inclusion mismatches for financial instruments;
• Has excessive PE deductions;
• Has multinational payee mismatches;
• Has made a counteraction or allocation of Dual Inclusion Income (DII).

Each mismatch category refers to specific sections of TIOPA 2010 and HMRC’s International Manual for technical definitions.

5. Statutory Clearance and the CT600B

In some cases, companies apply for statutory clearance from HMRC in relation to CFC rules under Part 9A TIOPA 2010 (or the old rules in ICTA 1988).

This clearance process:

• Is not mandatory, but can be sought for certainty on the tax treatment of a transaction;
• May be obtained before or after a transaction;
• Is typically handled by HMRC’s Clearance and Counteraction Team;
• Can confirm whether a CFC charge will arise in a specific scenario.

However, even if statutory clearance has been obtained confirming no CFC charge, the requirement to complete the CT600B can still apply.
This is because:

• The CT600B is used not only to declare CFC charges but also to confirm exemption claims;
• It is a compliance record showing HMRC that the CFC position has been considered for the relevant accounting period;
• In certain hybrid or foreign PE exemption cases, disclosure remains necessary regardless of clearance.

6. Practical Compliance Tips

Check exemptions early

Determining whether a foreign subsidiary qualifies for an exemption can save time and reduce compliance costs.

Retain clearance correspondence

Keep HMRC’s clearance letter as evidence to support your CT600B entries.

Coordinate group reporting

If multiple group companies hold interests in the same foreign entity, consolidate information to avoid inconsistencies.

Stay updated

The rules in TIOPA 2010 and HMRC guidance are subject to change; always refer to the most recent CT600B guidance notes on GOV.UK.

Conclusion

The CT600B is more than just a disclosure form — it is a compliance checkpoint ensuring UK companies with overseas interests are correctly applying the CFC rules, claiming valid exemptions, and reporting hybrid mismatches where required. While statutory clearance can provide comfort on the CFC position, it does not necessarily remove the requirement to complete the CT600B. Given the complexity of these rules and their interaction with transfer pricing and corporate structuring, professional advice is strongly recommended before filing.