CTM90605 | Corporation tax self-assessment (CTSA): Claims and elections: Quantification
From HM Revenue & Customs · Company Taxation Manual
says that a company must quantify all claims it makes for:
a relief,
an allowance, or
a repayment of tax,
at the time it makes the claim.
“Quantified” means that the company must express the claim in figures. It is not acceptable to express the claim as a formula.
This rule does not apply to elections because most of them cannot be quantified immediately.