IHTM30262 | Lifetime transfers chargeable when made: tax immediately payable
From HM Revenue & Customs · Inheritance Tax Manual
Instalments are available if the tax attributable to the qualifying property () is borne by the person benefiting from the transfer.
Accordingly instalments are not available:
if the transfer is grossed up ()or
if it is grossed up in part, to the extent that it is grossed up.