Gave land in commemoration of Nelson in 1905. Great nephew of Isaac Smith through whom, it seems likely, he may have inherited the land of Merton Abbey but how and when he acquired Merton Place and its grounds we don't know.
From the Conservation and Management Plan for Merton Priory we have learnt the location and extent of Merton Abbey (another word for Priory) and it was to the east of where we understand Merton Place and its grounds to have been.
Mackerell presumably knew of Merton Place and its high connections from early in life from visits to his family's neighbouring estate and perhaps he bought it because it was Nelson's and with the intention of giving some of it in commemoration of Nelson. Can't help but conjecture.