This stamp is listed in SG but unpriced. In Scott, it's listed O62, and in my 2014 edition, it's priced at $325. Could someone please give me a more up-to-date CV?
According to SG's SOTW 2018, this 1970 Official Stamps set is numbered O1040 to O1054. The 100p. green is O1054, and is showing £400 used, with £900 for mint.