CTM03580 | Corporation Tax: small profits relief: associated company - main rules of association
From HM Revenue & Customs · Company Taxation Manual
CTM03710 onwards gives detailed guidance on determining whether a company has an associated company or how many associated companies a company has during its accounting period. Note that
an associated company is counted even if it is an associated company for part only of an accounting period (but see CTM03640)
two or more associated companies are counted even if they are associated companies for different parts of the accounting period
an associated company which has not carried on any trade or business (see CTM03590) at any time during the accounting period is disregarded - if it is an associated company for part only of the accounting period, the rule applies to any time during that part.