Pollarding the plane tree in the Main Courtyard was mentioned in this blog on January 30. The strong "sculptural" impact of this is one of the main motivations. But pollarding also has some purely practical benefits. The height of the final tree is the first issue to consider.
The height to the top of the railing around the Wine Cellar is four metres and the final height of the pollarded tree probably shouldn't be more than twice that; that is around eight metres. Left to its own devices a London Plane could reach thirty metres or six times the current height of the tree!. This would overwhelm both the architecture and the Main Courtyard.
The first step in pollarding is to remove the central leader. It is then possible to start developing the characteristic candelabra form of a classic pollard.