You need to complete the CT600B Controlled foreign companies supplementary section if at any time during the accounting period reported the company held a relevant interest of 25% or more in a foreign company which is controlled from the UK. No controlled foreign company (CFC) need be included on CT600B where it satisfies the Excluded Countries Regulations.
A UK company may also include companies which may not be CFCs but which would satisfy one of the exemptions if they were. This applies to foreign companies which may not be subject to a lower level of tax, or may not be controlled from the UK. It also applies where the UK company's relevant interest in the foreign company may be less than 25%. The purpose of this is to save UK companies the cost of working out whether a foreign company is in principle a CFC in cases where it is clear that one of the exemptions would be passed if it were.
You also need to complete CT600B if the company is chargeable to the Bank Levy.
HMRC have provided following Company tax return guide to form CT600 (2020) Version 3 for accounting periods starting on or after 1 April 2015 to assist Companies complete the Corporation tax returns. Further information can also be found on GOV.UK website.