CTM97055 | Corporation Tax self assessment (CTSA): group relief - general: time limit - late claims
From HM Revenue & Customs · Company Taxation Manual
FA98/SCH18/PARA74 (2) lets HMRC extend the time limit for making and withdrawing group relief claims.
SP5/01 explains how HMRC exercises its existing discretion to admit late claims under CTSA.
See:
for the text of SP5/01
for more guidance on late claims.