In the 1951 Abbott sale it was mostly ancients with some British gold and a handful of silver. The coins were noted on the catalogue as being consigned by a family member, but I don't know the relationship. He was Australian, so it's more likely that his English silver was the Abbott 'Australian' collection acquired by Spink in 1951 according to the appendix in Manville and Robertson. But that raises the issue of Lockett dying in 1950, which is obviously earlier than 51. Doing a bit of digging, it appears that he was born in 1867 and died in Sydney on 7/11/1942, so it appears that Lockett was offered coins from the collection after his death and prior to the sale to Spink in 1951.
FWIW, the coin in question was the last coin in lot 163 (6) of Clonterbrook and one of 17 in Lockett II lot 2023, but no previous ownerships noted of any in the lot. That isn't very helpful I'm afraid.