IHTM35082 | How many variations can be attempted?: second variation affecting the same property
From HM Revenue & Customs · Inheritance Tax Manual
Our view that an instrument of variation (IoV) does not fall within IHTA84/S142 if it further redirects any item or part of an item that has already been redirected was upheld by Knox J in Russell v IRC (1988) STC 195. Accordingly where there has been an IoV accepted as within IHTA84/S142(1) there cannot be an IHTA84/S142(1) IoV
in relation to any part of the same property
in connection with the same death.
You should refer to Technical any case where this appears to apply, or any case in which there is an IoV and a disclaimer (whatever the order) affecting the same property on the same death.