CTM93060 | CTSA: the filing obligation: filing date: further time
From HM Revenue & Customs · Company Taxation Manual
Although the filing dates for the return are fixed by statute you do have the general power under TMA70/S118 (2) to:
allow further time for something to be done,
or
accept a reasonable excuse for failure to do something.
Note: These provisions operate in an `all or nothing’ way. They will either extinguish liability to a penalty, or not affect it at all.